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10 THE ROLE OF TROPOSPHERIC OZONE IN 

CLIMATE CHANGE AND UV-B EFFECTS

10.1 Introduction

1 Atmospheric O3 plays an important role in the Earth’s energy budget by interacting with 

2 incoming solar radiation and outgoing infrared radiation. Over mid-latitudes, 

3 approximately 90% of the total atmospheric O3 column is located in the stratosphere (Kar 

4 et al., 2010; Crist et al., 1994). Therefore, tropospheric O3 makes up a relatively small 

5 portion (~10%) of the total column of O3 over mid-latitudes, but it does play an 

6 important role in the overall radiation budget. The next section (Section 10.2) briefly 

7 describes the physics of the earth’s radiation budget, providing background material for 

8 the subsequent two sections assessing how perturbations in tropospheric O3 might affect 

9 (1) climate through its role as a greenhouse gas (Section 10.3), and (2) health, ecology 

10 and welfare through its role in shielding the earth’s surface from solar ultraviolet 

11 radiation (Section 10.4).

10.2 Physics of the Earth’s Radiation Budget

12 Radiant energy from the sun enters the atmosphere in a range of wavelengths, but peaks 

13 strongly in the visible (400 nm up to 750 nm) part of the spectrum. Longer wavelength 

14 infrared (750 nm up to ~1 mm) and shorter wavelength ultraviolet (400 nm down to 

15 100 nm) radiation are also present in the solar electromagnetic spectrum. Since the 

16 energy possessed by a photon is inversely proportional to its wavelength, infrared (IR) 

17 radiation carries the least energy per photon, and ultraviolet (UV) radiation carries the 

18 most energy per photon. UV radiation is further subdivided into classes based on 

19 wavelength: UV-A refers to wavelengths from 400-315 nm; UV-B from 315-280 nm; and 

20 UV-C from 280-100 nm. By the same argument above describing the relationship 

21 between photon wavelength and energy, UV-A radiation is the least energetic and UV-C 

22 is the most energetic band in the UV spectrum.

23 The wavelength of radiation also determines how the photons interact with the complex 

24 mixture of gases, clouds, and particles present in the atmosphere (see Figure 10-1). UV-A 

25 radiation can be scattered but is not absorbed to any meaningful degree by atmospheric 

26 gases including O3. UV-B radiation is absorbed and scattered in part within the 

27 atmosphere. UV-C is almost entirely blocked by the Earth’s upper atmosphere, where it 
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1 participates in photoionization and photodissociation processes including absorption by 

2 stratospheric O3.

Source: 2006 O3 AQCD.

Figure 10-1 Diagram of the factors that determine human exposure to 

ultraviolet radiation.

3 Since UV-A radiation is less energetic and does not interact with O3 in the troposphere or 

4 the stratosphere and UV-C radiation is almost entirely blocked by stratospheric O3, UV5 B radiation is the most important band to consider in relation to tropospheric O3

6 shielding. Furthermore, tropospheric O3 plays a “disproportionate” role in absorbing UV7 B radiation compared with stratospheric O3 on a molecule per molecule basis (Balis et 

8 al., 2002; Zerefos et al., 2002; Crist et al., 1994; Bruhl and Crutzen, 1989). This effect 

9 results from the higher atmospheric pressure present in the troposphere, resulting in 

10 higher concentrations of gas molecules present that can absorb or scatter radiation. For 

11 this reason, the troposphere is referred to as a “multiple scattering” regime for UV 

12 absorption, compared to the “single scattering” regime in the stratosphere. Thus, careful 

13 quantification of atmospheric absorbers and scatterers, along with a well-resolved 
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1 description of the physics of these interactions, is necessary for predicting the impact of 

2 tropospheric O3 on UV-B flux at the surface.

3 Solar flux at all wavelengths has a temporal dependence, while radiative scattering and 

4 absorption have strong wavelength, path length, and gas/particle concentration 

5 dependencies. These combine to create nonlinear effects on UV flux at the Earth’s 

6 surface. Chapter 10 of the 2006 O3 AQCD(U.S. EPA, 2006b) describes in detail several 

7 key factors that influence the spatiotemporal distribution of ground-level UV radiation 

8 flux, including: (1) long-term solar activity including sunspot cycle; (2) solar rotation; (3) 

9 the position of the Earth in its orbit around the sun; (4) atmospheric absorption and 

10 scattering of UV radiation by gas molecules and aerosol particles; (5) absorption and 

11 scattering by stratospheric and tropospheric clouds; and (6) surface albedo. The 

12 efficiencies of absorption and scattering are highly dependent on the concentration of the 

13 scattering medium, particle size (for aerosols and clouds), and the altitude at which these 

14 processes are occurring. These properties are sensitive to meteorology, which introduces 

15 additional elements of temporal dependency in ground-level UV radiation flux.

16 About 30% of incoming solar radiation is directly reflected back to space, mainly by 

17 clouds or surfaces with high albedo (reflectivity), such as snow, ice, and desert sand. 

18 Radiation that does penetrate to the Earth’s surface and is absorbed can be re-emitted in 

19 the longwave (infrared) portion of the spectrum (750 nm up to ~1 mm); the rest goes into 

20 evaporating water or soil moisture or emerges as sensible heat. The troposphere is opaque 

21 to the outgoing longwave radiation. Polyatomic gases such as CO2, CH4, and O3 absorb 

22 and re-emit the radiation upwelling from the Earth’s surface, reducing the efficiency with 

23 which that energy returns to space. In effect, these gases act as a blanket warming the 

24 Earth’s surface. This phenomenon, known as the “Greenhouse Effect,” was first 

quantified in the 19th 25 century (Arrhenius, 1896), and gives rise to the term “greenhouse 

26 gas.”

10.3 Effects of Tropospheric Ozone on Climate

Background

27 As a result of its interaction with incoming solar radiation and outgoing longwave 

28 radiation, tropospheric O3 is a major greenhouse gas, and increases in its abundance may 

29 contribute to climate change (IPCC, 2007b). Models estimate that the global average 

30 concentration of O3 in the troposphere has doubled since the preindustrial era (Gauss et 

31 al., 2006), while observations indicate that in some regions tropospheric O3 may have 
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1 increased by factors as great as 4 or 5 (Marenco et al., 1994; Staehelin et al., 1994). These 

2 increases are tied to the rise in emissions of O3 precursors from human activity, mainly 

3 fossil fuel consumption and agricultural processes.

4 The impact on climate of the tropospheric O3 change since preindustrial times has been 

5 estimated to be about 25-40% of anthropogenic CO2 impact and about 75% of 

6 anthropogenic CH4 impact (IPCC, 2007b), ranking it third in importance of the 

greenhouse gases. In the 21st 7 century as the Earth’s population continues to grow and 

8 energy technology spreads to developing countries, a further rise in the global 

9 concentration of tropospheric O3 is likely, with associated consequences for human 

10 health and ecosystems relating to climate change.

11 To examine the science of a changing climate and to provide balanced and rigorous 

12 information to policy makers, the World Meteorological Organization (WMO) and the 

13 United Nations Environment Programme (UNEP) formed the Intergovernmental Panel on 

14 Climate Change (IPCC) in 1988. The IPCC supports the work of the Conference of 

15 Parties (COP) to the United Nations Framework Convention on Climate Change 

16 (UNFCCC). The IPCC periodically brings together climate scientists from member 

17 countries of WMO and the United Nations to review knowledge of the physical climate 

18 system, past and future climate change, and evidence of human-induced climate change. 

19 IPCC climate assessment reports are issued every five to seven years.

20 This section draws in part on the fourth IPCC Assessment Report (AR4) (IPCC, 2007b), 

21 as well as other peer-reviewed published research. Section 10.3.1 reviews evidence of 

22 climate change in the recent past and projections of future climate change. It also offers a 

23 brief comparison of tropospheric O3 relative to other greenhouse gases. Section 10.3.2

24 describes factors that influence the magnitude of tropospheric O3 effects on climate. 

25 Section 10.3.3 considers the competing effects of O3 precursors on climate. Finally, 

26 Section 10.3.4 describes the effects of changing tropospheric O3 concentrations on 

27 present-day climate. Downstream effects resulting from climate change, such as 

28 ecosystem responses, are outside the scope of this assessment, which focuses on the 

29 direct effects of tropospheric O3 on climate.

10.3.1 Climate Change Evidence and the Influence of Tropospheric Ozone

10.3.1.1 Climate Change in the Recent Past

30 From the end of the Last Ice Age 12,000 years ago until the mid-1800s, observations 

31 from ice cores show that concentrations of the long-lived greenhouse gases CO2, CH4, 
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1 and N2O have been relatively stable. Unlike these greenhouse gases, O3 is not preserved 

2 in ice, and no record of it before the late 1800s exists. Models, however, suggest that it, 

3 too, has remained relatively constant during this time period (Thompson et al., 1993; 

4 Thompson, 1992). The stable mix of greenhouse gases in the atmosphere has kept the 

5 global mean temperature of the Earth close to 15oC. Without the presence of greenhouse 

6 gases in the atmosphere, the Earth’s temperature would be about 30oC cooler, or -15oC.

7 Since the start of the Industrial Revolution, human activity has led to significant increases 

8 of greenhouse gases in the atmosphere, mainly through fossil fuel combustion. According 

9 to the IPCC AR4 (IPCC, 2007b), there is now “very high confidence” that the net effect 

10 of anthropogenic greenhouse gas emissions since 1750 has led to warming, and it is “very 

11 likely” that human activity contributed to the 0.76oC rise in global mean temperature 

12 observed over the last century. The increase of tropospheric O3 may have contributed 

13 0.1-0.3oC warming to the global climate during this time period (Hansen et al., 2005; 

14 Mickley et al., 2004). Global cooling due to anthropogenic aerosols (IPCC, 2007b) has 

15 likely masked the full warming effect of the anthropogenic greenhouse gases. Emissions 

16 of aerosols and their precursors in the United States and other developed countries are 

17 presently decreasing rapidly due to regulatory policies. The consequences of such 

18 decreases on regional climate could be large, as indicated by observations (e.g., Philipona 

19 et al., 2009; Ruckstuhl et al., 2008) and models (e.g., Kloster et al., 2009; Mickley et al., 

20 In Press).

10.3.1.2 Projections of Future Climate Change

The IPCC AR4 projects a warming of ~0.2oC per decade for the remainder of the 21st 21

22 century (IPCC, 2007b). Even at constant concentrations of greenhouse gases in the 

23 atmosphere, temperatures are expected to increase by about 0.1oC per decade, due to the 

24 slow response of oceans to the warming applied so far. It is likely that the Earth will 

experience longer and more frequent heat waves in the 21st 25 century, together with more 

26 frequent droughts and/or heavy precipitation events in some regions, due to perturbations 

27 in the hydrological cycle that result from changing temperatures (IPCC, 2007b). Sea 

28 levels could increase by 0.3-0.8 m by 2300 due to thermal expansion of the oceans. The 

29 extent of Arctic sea ice is expected to decline, and contraction of the Greenland ice sheet 

30 could further contribute to the sea level rise (IPCC, 2007b).

31 Projections of future climate change are all associated with some degree of uncertainty. A 

32 major uncertainty involves future trends in the anthropogenic emissions of greenhouse 

33 gases or their precursors. For the IPCC AR4 climate projections, a set of distinct 

34 “storylines” or emission pathways was developed (IPCC, 2000). Each storyline took into 
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1 account factors such as population growth, mix of energy technologies, and the sharing of 

2 technology between developed and developing nations, and each resulted in a different 

3 scenario for anthropogenic emissions. When these trends in emissions are applied to 

models, these scenarios yield a broad range of possible climate trajectories for the 21st 4

5 century.

6 A second factor bringing large uncertainty to model projections of future climate is the 

7 representation of climate and, especially, climate feedbacks. A rise in surface 

8 temperatures would perturb a suite of other processes in the earth-atmosphere-ocean 

9 system, which may in turn either amplify the temperature increase (positive feedback) or 

10 diminish it (negative feedback). One important feedback involves the increase of water 

11 vapor content of the atmosphere that would accompany higher temperatures (Bony et al., 

12 2006). Water vapor is a potent greenhouse gas; accounting for the water vapor feedback 

13 may increase the climate sensitivity to a doubling of CO2 by nearly a factor of two (Held 

14 and Soden, 2000). The ice-albedo feedback is also strongly positive; a decline in snow 

15 cover and sea ice extent would diminish the Earth’s albedo, allowing more solar energy 

16 to be deposited to the surface (Holland and Bitz, 2003; Rind et al., 1995). A final 

17 example of a climate feedback involves the effects of changing cloud cover in a warming 

18 atmosphere. Models disagree on the magnitude and even the sign of this feedback on 

19 surface temperatures (Soden and Held, 2006).

10.3.1.3 Metrics of Potential Climate Change

20 Two different metrics are frequently used to estimate the potential climate impact of 

21 some perturbation such as a change in greenhouse gas concentration: (1) radiative 

22 forcing; and (2) global warming potential (GWP).

23 Radiative forcing is a change in the radiative balance at a particular level of the 

24 atmosphere or at the surface when a perturbation is introduced in the earth-atmosphere25 ocean system. In the global mean, radiative forcing of greenhouse gases at the tropopause 

26 (top of the troposphere) is roughly proportional to the surface temperature response 

27 (Hansen et al., 2005; NRC, 2005). It thus provides a useful metric for policymakers for 

28 assessing the response of the earth’s surface temperature to a given change in the 

29 concentration of a greenhouse gas. Positive values of radiative forcing indicate warming 

30 in a test case relative to the control; negative values indicate cooling. The units of 

radiative forcing are energy flux per area, or W/m2 31 .

32 Radiative forcing requires just a few model years to calculate, and it shows consistency 

33 from model to model. However, radiative forcing does not take into account the climate 

34 feedbacks that could amplify or dampen the actual surface temperature response, 
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1 depending on region. Quantifying the change in surface temperature requires a climate 

2 simulation in which all important feedbacks are accounted for. As these processes are not 

3 well understood, the surface temperature response to a given radiative forcing is highly 

4 uncertain and can vary greatly among models and even from region to region within the 

5 same model.

6 GWP indicates the integrated radiative forcing over a specified period (usually 100 years) 

7 from a unit mass pulse emission of a greenhouse gas or its precursor, and are reported as 

8 the magnitude of this radiative forcing relative to that of CO2. GWP is most useful for 

9 comparing the potential climate impacts of long-lived gases, such as N2O or CH4. Since 

10 tropospheric O3 has a lifetime on the order of weeks to months, GWP is not seen as a 

11 valuable metric for quantifying the importance of O3 on climate (Forster et al., 2007).

10.3.1.4 Tropospheric Ozone as a Greenhouse Gas

12 Tropospheric O3 differs in important ways from other greenhouse gases. It is not emitted 

13 directly, but is produced through photochemical oxidation of CO, CH4, and nonmethane 

14 volatile organic compounds (VOCs) in the presence of nitrogen oxide radicals (NOX = 

15 NO + NO2; see Section 3.2 for further details on the chemistry of O3 formation). It is also 

16 supplied by vertical transport from the stratosphere. The lifetime of O3 in the troposphere 

17 is typically a few weeks, resulting in an inhomogeneous distribution that varies 

18 seasonally; the distribution of the long-lived greenhouse gases like CO2 and CH4 are 

19 much more uniform. The longwave radiative forcing by O3 is mainly due to absorption in 

20 the 9.6 μm window, where absorption by water vapor is weak. It is therefore less 

21 sensitive to local humidity than the radiative forcing by CO2 or CH4, for which there is 

22 much more overlap with the water absorption bands (Lenoble, 1993). And unlike other 

23 major greenhouse gases, O3 absorbs in the shortwave as well as the longwave part of the 

24 spectrum.

25 Figure 10-2 shows the main steps involved in the influence of tropospheric O3 on 

26 climate. Emissions of O3 precursors including CO, VOCs, CH4, and NOX lead to 

27 production of tropospheric O3. A change in the abundance of tropospheric O3 perturbs 

28 the radiative balance of the atmosphere, an effect quantified by the radiative forcing 

29 metric. The earth-atmosphere-ocean system responds to the radiative forcing with a 

30 climate response, typically expressed as a change in surface temperature. Finally, the 

31 climate response causes downstream climate-related health and ecosystem impacts, such 

32 as redistribution of diseases or ecosystem characteristics due to temperature changes. 

33 Feedbacks from both the climate response and downstream impacts can, in turn, affect 

34 the abundance of tropospheric O3 and O3 precursors through multiple feedback 
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1 mechanisms. Direct feedbacks are discussed further in Section 10.3.3.4; the downstream 

2 climate impacts and their feedbacks are extremely complex and outside the scope of this 

3 assessment.

Figure 10-2 Schematic illustrating the effects of tropospheric ozone on climate.

Figure includes the relationship between precursor emissions, 

tropospheric ozone abundance, radiative forcing, climate response, 

and climate impacts. Units shown are those typical for each 

quantity illustrated. Feedbacks from both the climate response and

climate impacts can, in turn, affect the abundance of tropospheric 

ozone and ozone precursors through multiple feedback 

mechanisms. Climate impacts are deemphasized in the figure since 

these downstream effects are extremely complex and outside the 

scope of this assessment.

The IPCC (2007b) reported a radiative forcing of 0.35 W/m2 4 for the change in 

5 tropospheric O3 since the preindustrial era, ranking it third in importance after the 

greenhouse gases CO2 (1.66 W/m2) and CH4 (0.48 W/m2 6 ). Figure 10-3 shows the global 

7 average radiative forcing estimates and uncertainty ranges in 2005 for anthropogenic 

8 CO2, CH4, O3 and other important agents and mechanisms. The error bars encompassing 
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the tropospheric O3 radiative forcing estimate in the figure range from 0.25 to 0.65 W/m2 1 , 

2 making it relatively more uncertain than the long-lived greenhouse gases.

Source: Used with permission from Cambridge University Press, IPCC (2007b)

Figure 10-3 Global average radiative forcing (RF) estimates and uncertainty 

ranges in 2005 for anthropogenic CO2, CH4, ozone and other 

important agents and mechanisms. Figure shows the typical 

geographical extent (spatial scale) of the radiative forcing and the 

assessed level of scientific understanding (LOSU). The net 

anthropogenic radiative forcing and its range are also shown. 

These require summing asymmetric uncertainty estimates from the 

component terms, and cannot be obtained by simple addition. 

Additional radiative forcing factors not included here are 

considered to have a very low LOSU.
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10.3.2 Factors that Influence the Effect of Tropospheric Ozone on Climate

1 This section describes the main factors that influence the magnitude of the climate 

2 response to changes in tropospheric O3. They include: (1) trends in the concentration of 

3 tropospheric O3; (2) the effect of surface albedo on O3 radiative forcing; (3) the effect of 

4 vertical distribution on O3 radiative forcing; (4) feedback factors that can alter the climate 

5 response to O3 radiative forcing; and (5) the indirect effects of tropospheric O3 on the 

6 carbon cycle. Trends in stratospheric O3 may also affect temperatures at the Earth’s 

7 surface, but aside from issues relating STE discussed in Chapter 3, Section 3.4.2, 

8 stratospheric O3 assessment is beyond the scope of this document.

10.3.2.1 Trends in the Concentration of Tropospheric Ozone

9 To first order, the effect of tropospheric O3 on climate is proportional to the change in 

10 tropospheric O3 concentration. The earth’s surface temperatures are most sensitive to O3

11 perturbations in the mid to upper troposphere. This section therefore focuses mainly on 

12 observed O3 trends in the free troposphere or in regions far from O3 sources, where a 

13 change in O3 concentrations may indicate change throughout the troposphere. Data from 

14 ozonesondes, mountaintops, and remote surface sites are discussed, as well as satellite 

15 data.

Observed Trends in Ozone Since the Preindustrial Era

16 Measurements of O3 at two European mountain sites dating from the late 1800s to early 

17 1900s show values at about 10 ppb, about one-fifth the values observed today at similar 

18 sites (Pavelin et al., 1999; Marenco et al., 1994). The accuracy of these early 

19 measurements is questionable however, in part because they exhibit O3 concentrations 

20 equivalent to or only a couple of parts per billion greater than those observed at nearby 

21 low-altitude sites during the same time period (Mickley et al., 2001; Volz and Kley, 

22 1988). A larger vertical gradient in tropospheric O3 would be expected because of its 

23 stratospheric source and its longer lifetime aloft. In another study, Staehelin et al. (1994)

24 revisited observations made in the Swiss mountains during the 1950s and found a 

25 doubling in O3 concentrations from that era to 1989-1991.

26 Routine observations of O3 in the troposphere began in the 1970s with the use of balloon27 borne ozonesondes, but even this record is sparse. Trends from ozonesondes have been 

28 highly variable and dependent on region (Logan et al., 1999). Over most sites in the U.S., 

29 ozonesondes reveal little trend. Over Canada, observations show a decline in O3 between 

30 1980 and 1990, then a rebound in the following decade (Tarasick et al., 2005). 
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1 Ozonesondes over Europe give a mixed picture. European ozonesondes showed 

2 significant increases in the 1970s and 1980s, with smaller increases or even declines 

3 since then (Oltmans et al., 2006; Logan et al., 1999). Over Japan, O3 in the lower 

4 troposphere increased about 0.2-0.4 ppb/y during the 1990s (Naja and Akimoto, 2004).

5 Ground-based measurements in remote regions provide a record of tropospheric O3

6 extending as far back as the late 1960s or, for ship measurements, the late 1970s. A long7 term record of O3 in the San Bernardino Mountains of California reveals that the number 

8 of high O3 days (defined as days with daily maximum O3 levels above 95 ppb) rose from 

9 about 100 per summer in 1969 to over 160 in 1978 (Lee et al., 2003a). Over the next 20 

10 years, the number of high O3 days dropped slowly, to well below 100 per summer by the 

11 end of the record in 1999. Springtime O3 observations from several other mountain sites 

12 in the western U.S. show a positive trend of about of 0.5-0.7 ppb/y since the 1980s 

13 (Cooper et al., 2010; Jaffe et al., 2003). Ship-borne O3 measurements for the time period 

14 1977 to 2002 indicate increases of 0.1-0.7 ppb/y over the tropical and South Atlantic, but 

15 no significant change over the North Atlantic (Lelieveld et al., 2004). The lack of trend 

16 for the North Atlantic would seem at odds with O3 observations at Mace Head on the 

17 west coast of Ireland, which show a significant positive trend of about 0.5 ppb/y from 

18 1987 to 2003 (Simmonds et al., 2004). Over Japan, O3 at a remote mountain site has 

19 increased 1 ppb/y from 1998 to 2003 (Tanimoto, 2009), a rate more than double that 

20 recorded by ozonesondes in the lower troposphere over Japan during the 1990s (Naja and 

21 Akimoto, 2004). At Zugspitze, a mountain site in Germany, O3 increased by 12% per 

22 decade during the 1970s and 1980s, consistent with European ozonesondes (Oltmans et 

23 al., 2006). Since then, O3 continues to increase at Zugspitze, but more slowly. What little 

24 data exist for the Southern Hemisphere point to significant increases in tropospheric O3

25 in recent decades, as much as ~15% at Cape Grim in the 1989-2004 time period (Oltmans 

26 et al., 2006).

27 The satellite record is now approaching a length that can be useful for diagnosing trends 

28 in the total tropospheric O3 column (details on the use of satellites to measure 

29 tropospheric O3 are covered in Section 3.5.5.5). In contrast to the surface data from ships, 

30 tropospheric O3 columns from the Total Ozone Mapping Spectrometer (TOMS) show no 

31 trend over the tropical Atlantic for the period 1980-1990 (Thompson and Hudson, 1999). 

32 Over the Pacific, a longer, 25 year record of TOMS data again reveals no trend over the 

tropics, but shows increases in tropospheric column O3 of about 2-3 Dobson Units (DU)1 33

34 at midlatitudes in both hemispheres (Ziemke et al., 2005).

 1 The Dobson Unit is a typical unit of measure for the total O3 in a vertical column above the Earth’s surface. One DU is equivalent 

to the amount of O3 that would exist in a 1 μm (10–5 m) thick layer of pure O3 at standard temperature (0oC) and pressure (1 atm), 

and corresponds to a column of O3 containing 2.69 x 1020 molecules/m2

. A typical value for the amount of ozone in a column of the 

Earth’s atmosphere, although highly variable, is 300 DU and approximately 10% (30 DU) of that exists in the troposphere at mid 

latitudes.
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1 Interpreting these recent trends in tropospheric O3 is challenging. The first difficulty is 

2 reconciling apparently contradictory trends in the observations, e.g., over tropical oceans. 

A second difficulty is that the O3 3 trends depend on several factors, not all of which can be 

4 well characterized. These factors include (1) trends in emissions of O3 precursors, (2) 

5 variation in the stratospheric source of O3, (3) changes in solar radiation resulting from 

6 stratospheric O3 depletion, and (4) trends in tropospheric temperatures (Fusco and Logan, 

7 2003). The trends in O3 in the San Bernardino Mountains reported by Lee et al. (2003a)

8 likely reflects regional increases in population and motor vehicles usage, and subsequent 

9 implementation of more stringent motor vehicle emissions controls. More recent positive 

10 trends in the western U.S. and over Japan are consistent with the rapid increase in 

11 emissions of O3 precursors from mainland Asia and transport of pollution across the 

12 Pacific (Cooper et al., 2010; Tanimoto, 2009). The satellite trends over the northern mid13 latitudes are consistent with this picture as well (Ziemke et al., 2005). Increases in 

14 tropospheric O3 in the Southern Hemisphere are also likely due to increased 

15 anthropogenic NOX emissions, especially from biomass burning (Fishman et al., 1991). 

16 Recent declines in summertime O3 over Europe can be partly explained by decreases in 

17 O3 precursor emissions there (Jonson et al., 2005), while springtime increases at some 

18 European sites are likely linked to changes in stratospheric dynamics (Ordonez et al., 

19 2007). Over Canada, Fusco and Logan (2003) found that O3 depletion in the lowermost 

20 stratosphere may have reduced the stratospheric flux of O3 into the troposphere by as 

21 much as 30% from the early 1970s to the mid 1990s, consistent with the trends in 

22 ozonesondes there.

Calculation of Ozone Trends for the Recent Past

23 Attempts to simulate trends in tropospheric O3 allow us to test current knowledge of O3

24 processes and to predict with greater confidence trends in future O3 concentrations. 

25 Time-dependent emission inventories of O3 precursors have also been developed (for 

26 1850-2000, Lamarque et al., 2010; for 1890-1990, Van Aardenne et al., 2001). These 

27 inventories allow for the calculation of changing O3 concentration over time.

28 One recent multi-model study calculated an increase in the O3 concentration since 

29 preindustrial times of 8-14 DU, or about 30-70% (Gauss et al., 2006). The large spread in 

30 modeled estimates reveals our limited knowledge of processes in the pristine atmosphere. 

31 Models typically overestimate the late nineteenth and early twentieth century 

32 observations available in surface air and at mountain sites by 50-100% (Lamarque et al., 

33 2005; Shindell et al., 2003; Mickley et al., 2001; Kiehl et al., 1999). Reconciling the 

34 differences between models and measurements will require more accurate simulation of 

35 the natural sources of O3 (Mickley et al., 2001) and/or implementation of novel sinks 
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1 such as bromine radicals, which may reduce background O3 in the pristine atmosphere by 

2 as much as 30% (Yang et al., 2005c).

3 For the more recent past (since 1970), application of time-dependent emissions reveals an 

4 equatorward shift in the distribution of tropospheric O3 in the Northern Hemisphere due 

5 to the industrialization of societies at low-latitudes (Lamarque et al., 2005; Berntsen et 

6 al., 2000). By constraining a model with historical (1950s-2000) observations, Shindell et 

7 al. (2002) calculated a large increase of 8.2 DU in tropospheric O3 over polluted 

8 continental regions since 1950. Their result appears consistent with the large change in 

9 tropospheric O3 since preindustrial times implied by the observations from the late 1800s 

10 (Pavelin et al., 1999; Marenco et al., 1994).

10.3.2.2 The Effect of Surface Albedo on Ozone Radiative Forcing

11 The Earth’s surface albedo plays a role in O3 radiative forcing. Through most of the 

12 troposphere, absorption of incoming shortwave solar radiation by O3 is small relative to 

13 its absorption of outgoing longwave terrestrial radiation. However, over surfaces 

14 characterized by high albedo (e.g., over snow, ice, or desert sand), incoming radiation is 

15 more likely to be reflected than over darker surfaces, and the probability that O3 will 

16 absorb shortwave solar radiation is therefore larger. In other words, energy that would 

17 otherwise return to space may instead be deposited in the atmosphere. Several studies 

18 have shown that transport of O3 to the Arctic from mid-latitudes leads to radiative forcing 

estimates greater than 1.0 W/m2 19 in the region, especially in summer (Shindell et al., 2006; 

20 Liao et al., 2004b; Mickley et al., 1999). Because the Arctic is especially sensitive to 

21 radiative forcing through the ice-albedo feedback, the large contribution in the shortwave 

22 solar spectrum to the total radiative forcing in the region may be important.

10.3.2.3 The Effect of Vertical Distribution on Ozone Radiative 

Forcing

23 In the absence of feedbacks, O3 increments near the tropopause produce the largest 

24 increases in surface temperature (Lacis et al., 1990; Wang et al., 1980). This is a result of 

25 the colder temperature of the tropopause relative to the rest of the troposphere and 

26 stratosphere. Since radiation emitted by the atmosphere is approximately proportional to 

the fourth power of its temperature2 27 , the colder the added O3 is relative to the earth’s 

 2 As described by the Stefan-Boltzmann law, an ideal blackbody--which the atmosphere approximates--absorbs at all wavelengths

and re-radiates proportional to the fourth power of its temperature.
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1 surface, the weaker the radiation emitted and the greater the “trapping” of longwave 

2 radiation in the troposphere.

10.3.2.4 Feedback Factors that Alter the Climate Response to 

Changes in Ozone Radiative Forcing

3 Estimates of radiative forcing provide a first-order assessment of the effect of 

4 tropospheric O3 on climate. In the atmosphere, climate feedbacks and transport of heat 

5 alter the sensitivity of Earth’s surface temperature to addition of tropospheric O3. 

6 Assessment of the full climate response to increases in tropospheric O3 requires use of a 

7 climate model to simulate these interactions.

8 Due to its short lifetime, O3 is heterogeneously distributed through the troposphere. 

9 Sharp horizontal gradients exist in the radiative forcing of O3, with the greatest radiative 

10 forcing since preindustrial times occurring over the northern mid-latitudes (more on this 

11 in Section 10.3.4). If climate feedbacks are particularly powerful, they may obscure or 

12 even erase the correlation between regional radiative forcing and climate response 

13 (Harvey, 2004; Boer and Yu, 2003). For example, several model studies have reported 

14 that the horizontal pattern of surface temperature response from 2000-2100 trends in 

15 predicted short-lived species (including O3) closely matches the pattern from the trends 

16 in the long-lived greenhouse gases over the same time period (Levy et al., 2008; Shindell 

17 et al., 2008; Shindell et al., 2007). This correspondence occurs even though the patterns 

18 of radiative forcing for the short-lived and long-lived species differ significantly. In a 

19 separate paper, Shindell (2007) found that Arctic temperatures are especially sensitive to 

20 the mid-latitude radiative forcing from tropospheric O3.

21 Other studies have found that the signature of warming due to tropospheric O3 does show 

22 some consistency with the O3 radiative forcing. For example, Mickley et al. (2004)

23 examined the change in O3 since preindustrial times and found greater warming in the 

24 Northern Hemisphere than in the Southern Hemisphere (+0.4oC versus +0.2oC), as well 

25 as higher surface temperatures downwind of Europe and Asia and over the North 

26 American interior in summer. For an array of short-lived species including O3, Shindell 

27 and Faluvegi (2009) found that radiative forcing applied over northern mid-latitudes yield 

28 more localized responses due to local cloud, water vapor, and albedo feedbacks than 

29 radiative forcing applied over the tropics.

30 Climate feedbacks can also alter the sensitivity of surface temperature to the vertical 

31 distribution of tropospheric O3. The previous section (Section 10.3.2.3) described the 

32 greater impact of O3 added to the upper troposphere (near the tropopause) on radiative 

33 forcing, relative to additions in the mid- to lower troposphere. However, warming 
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1 induced by increased O3 in the upper troposphere could stabilize the atmosphere to some 

2 extent, limiting the transport of heat to the Earth’s surface and mitigating the impact of 

3 the added O3 on surface temperature (Joshi et al., 2003; Christiansen, 1999). Hansen et 

4 al. (1997) determined that allowing cloud feedbacks in a climate model meant that O3

5 enhancements in the mid-troposphere had the greatest effect on surface temperature.

6 Finally, climate feedbacks can amplify or diminish the climate response of one 

7 greenhouse gas relative to another. For example, Mickley et al. (2004) found a greater 

8 temperature response to CO2 radiative forcing than to an O3 radiative forcing of similar 

9 global mean magnitude, due in part to the relatively weak ice-albedo feedback for O3. 

10 Since CO2 absorbs in the same bands as water vapor, CO2 radiative forcing saturates in 

11 the middle troposphere and is also shifted toward the drier poles. A poleward shift in 

12 radiative forcing amplifies the ice-albedo feedback in the case of CO2, and the greater 

13 mid-troposphere radiative forcing allows for greater surface temperature response, 

14 relative to that for O3.

10.3.2.5 Indirect Effects of Tropospheric Ozone on the Carbon Cycle

15 A proposed indirect effect of tropospheric O3 on climate involves the carbon cycle. By 

16 directly damaging plant life in ways discussed in Chapter 9, increases in tropospheric O3

17 may depress the land-carbon sink of CO2, leading to accumulation of CO2 in the 

18 atmosphere and ultimately warming of the Earth’s surface. Sitch et al. (2007) calculated 

19 that this indirect warming effect of O3 on climate has about the same magnitude as the 

20 O3 direct effect. Their results suggest a doubled sensitivity of surface temperatures to O3

21 radiative forcing, compared to current model estimates.

10.3.3 Competing Effects of Ozone Precursors on Climate

22 Changes in O3 precursors affect not just O3 concentrations, but also other species that 

23 have importance to the radiative balance of the earth’s climate system. More specifically, 

24 O3 and its precursors exert a strong control on the oxidizing capacity of the troposphere 

25 (Derwent et al., 2001). For example, an increase in CO or VOCs would lead to a decrease 

26 in hydroxyl (OH) concentrations. Since OH is a major sink of the greenhouse gas CH4, a 

27 decline in OH would lengthen the CH4 lifetime, enhance the CH4 concentration, and 

28 amplify surface warming. A rise in NOX emissions, on the other hand, could lead to an 

29 increase in OH in certain locations, shortening the CH4 lifetime and leading to surface 

30 cooling (Fuglestvedt et al., 1999). O3 can itself generate OH through (1) photolysis 
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1 leading to excited oxygen atoms followed by reaction with water vapor and (2) reaction 

2 with HO2. 

3 Analyzing the net radiative forcing per unit emission for a suite of O3 precursors, 

Shindell and Faluvegi (2009) calculated positive (+0.25 W/m2 4 ) radiative forcing from the 

5 increase in anthropogenic emissions of CO and VOCs since preindustrial times, as well 

as for CH4 (+1 W/m2 6 ). These species also contribute to warming via their eventual 

7 contribution to CO2. In contrast, Shindell and Faluvegi (2009) found negative (-

0.29 W/m2 8 ) radiative forcing from anthropogenic emissions of NOX due mainly to the 

9 link between NOX and CH4. These results are consistent with those of Forster et al. 

(2007) who reported a net warming of +0.27 W/m2 10 for combined anthropogenic CO and 

VOCs emissions and a net cooling of -0.21 W/m2 11 for anthropogenic NOX emissions. 

12 Other studies have found a near cancellation of the positive O3 radiative forcing and the 

13 negative CH4 radiative forcing that arise from an incremental increase in anthropogenic 

14 NOX emissions (Naik et al., 2005; Fiore et al., 2002; Fuglestvedt et al., 1999).

15 The net effect of aircraft NOX on climate is complex. While Isaksen et al. (2001) reported 

16 that the net radiative forcing effect of aircraft NO emissions is near zero, Wild et al. 

17 (2001) calculated a net warming due to increased O3 production efficiency in the upper 

18 troposphere. More recently, Stevenson et al. (2004) completed a detailed analysis of the 

19 OH budget in the years following a pulse of aircraft NOX emissions. They calculated that 

20 while such a pulse leads initially to warming through O3 production over a few months, 

21 the long-term effect is cooling through the effects on CH4. Both aircraft NOX and the O3

22 it generates enhance OH concentrations, with the longer-lived O3 responsible for 

23 transferring the oxidizing effects of aircraft emissions away from flight corridors. 

24 Finally, OH production from O3 precursors can affect regional sulfate air quality and 

25 climate forcing by increasing gas-phase oxidation rates of SO2. Using the A1B scenario 

26 in the IPCC AR4, Unger et al. (2006) reported that at 2030, enhanced OH from the A1B 

27 O3 precursors increased surface sulfate aerosol concentrations by up to 20% over India 

28 and China, relative to the present-day, with a corresponding increase in radiative cooling 

29 over these regions. In this way, O3 precursors may impose an indirect cooling via sulfate 

30 (Unger, 2006).

31 Taken together, these results point out the need for careful assessment of net radiative 

32 forcing involving multiple pollutants in developing climate change policy (Unger et al., 

33 2008). Naik et al. (2005) calculated that a carefully combined reduction of CO, VOCs, 

34 and NOX emissions could lead to net cooling, especially over the tropics. Several studies 

35 point to CH4 as a particularly attractive target for emissions control since CH4 is itself an 

36 important precursor of O3 (West et al., 2007; Fiore et al., 2002). Shindell et al. (2005)

37 calculated that the emissions-based radiative forcing of anthropogenic CH4, which 
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includes both its own radiative forcing and that of CH4-generated O3, is 0.8-0.9 W/m2 1 , 

2 about double that of the CH4 abundance-based radiative forcing. Fiore et al. (2002) found

3 that reducing anthropogenic CH4 emissions by 50% would lead to a global negative (-

0.37 W/m2 4 ) radiative forcing, mostly from CH4. In later research, Fiore et al. (2008)

5 reported that CH4 reductions would most strongly affect tropospheric O3 column 

6 amounts in a zonal band centered around 30 N, a region of strong downwelling and NOX7 saturated conditions near the surface.

10.3.4 Calculating Radiative Forcing and Climate Response to Past Trends 

in Tropospheric Ozone

8 The magnitude of the radiative forcing from the change in tropospheric O3 since the 

9 preindustrial era is uncertain. This uncertainty derives in part from the scarcity of early 

10 measurements and in part from our limited knowledge regarding processes in the natural 

atmosphere. As noted previously, the IPCC AR4 reports a radiative forcing of 0.35 W/m2 11

12 from the change in tropospheric O3 since 1750 (Forster et al., 2007), ranking it third in 

13 importance among greenhouse gases after CO2 and CH4. The O3 radiative forcing could, 

in fact, be as large as 0.7 W/m2, if reconstructions of preindustrial and mid-20th 14 century 

15 O3 based on the measurement record are valid (Shindell and Faluvegi, 2002; Mickley et 

16 al., 2001). In any event, Unger et al. (2010) showed that present-day O3 radiative forcing 

17 can be attributed to emissions from many economic sectors, including on-road vehicles, 

18 household biofuel, power generation, and biomass burning. As much as one-third of the 

19 radiative forcing from the 1890 to 1990 change in tropospheric O3 could be due to 

20 increased biomass burning (Ito et al., 2007a).

21 These calculated radiative forcing estimates can be compared to those obtained from 

22 satellite data. Using data from TOMS, Worden et al. (2008) estimated a reduction in 

clear-sky outgoing longwave radiation of 0.48 W/m2 23 by O3 in the upper troposphere over 

24 oceans in 2006. This radiative forcing includes contributions from both anthropogenic 

25 and natural O3. Assuming that the concentration of O3 has roughly doubled since 

26 preindustrial times (Gauss et al., 2006), the total O3 radiative forcing estimated with 

27 TOMS is consistent with that obtained from models estimating just the anthropogenic 

28 contribution.

29 Calculation of the climate response to the O3 radiative forcing is challenging due to 

30 complexity of feedbacks, as mentioned in Sections 10.3.1.2 and 10.3.2.4. In their 

31 modeling study, Mickley et al. (2004) reported a global mean increase of 0.28oC since 

32 preindustrial times, with values as large as 0.8oC in continental interiors. For the time 

33 period since 1870, Hansen et al. (2005) estimated a much smaller increase in global mean 
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1 surface temperature (0.11oC), but they implemented 1880s anthropogenic emissions in 

2 their base simulation and also took into account trends in both stratospheric and 

3 tropospheric O3; the modeled decline of lower stratospheric O3, especially over polar 

4 regions, cooled surface temperatures in this study, counteracting the warming effect of 

5 increasing tropospheric O3.

6 Figure 10-4 shows the Hansen et al. (2005) results as reported in Shindell et al. (2006). In 

7 that figure, summertime O3 has the largest radiative impact over the continental interiors 

8 of the Northern Hemisphere. Shindell et al. (2006) estimated that the change in 

tropospheric O3 over the 20th 9 century could have contributed about 0.3oC to annual mean 

10 Arctic warming and as much as 0.4-0.5oC during winter and spring. Over eastern China, 

11 Chang et al. (2009) calculated a surface temperature increase of 0.4oC to the 1970-2000 

12 change in tropospheric O3. It is not clear, however, to what degree regional changes in 

13 O3 concentration influenced this response, as opposed to more global changes.
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Source: Used with permission from American Geophysical Union (Shindell et al., 2006)

Figure includes the input radiative forcing (W/m2

), as computed by the NASA GISS chemistry-climate model. Values are surface 

temperature trends for the annual average (top left), June–August (bottom left), and December-February (bottom right) and annual 

average tropopause instantaneous radiative forcing from 1880 to 1990 (top right). Temperature trends greater than about 0.1oC are 

significant over the oceans, while values greater than 0.3oC are typically significant over land, except for northern middle and high 

latitudes during winter where values in excess of about 0.5oC are significant. Values in the top right corner give area-weighted global 

averages in the same units as the plots.

Figure 10-4 Ensemble average 1900-2000 surface temperature trends (oC per 

century) in response to tropospheric ozone changes.

10.4 UV-B Related Effects and Tropospheric Ozone

10.4.1 Background

1 UV radiation emitted from the Sun contains sufficient energy when it reaches the Earth to 

2 break (photolyze) chemical bonds in molecules, thereby leading to damaging effects on 

3 living organisms and materials. Atmospheric O3 plays a crucial role in reducing exposure 

4 to solar UV radiation at the Earth’s surface. Stratospheric O3 is responsible for the 

5 majority of this shielding effect, as approximately 90% of total atmospheric O3 is located 

6 there over mid-latitudes (Kar et al., 2010; Crist et al., 1994). Investigation of the 
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1 supplemental shielding of UV-B radiation provided by tropospheric O3 is necessary for 

2 quantifying UV-B exposure and the incidence of related human health effects, ecosystem 

3 effects, and materials damage. The role of tropospheric O3 in shielding of UV-B radiation 

4 is discussed in this section.

10.4.2 Human Exposure and Susceptibility to Ultraviolet Radiation

5 The factors that potentially influence UV radiation exposure were discussed in detail in 

6 Chapter 10 of the 2006 O3 AQCD and are summarized here. These factors included 

7 outdoor activity, occupation, age, gender, geography, and protective behavior. Outdoor 

8 activity and occupation both influenced the amount of time people spend outdoors during 

9 daylight hours, the predominant factor for exposure to solar UV radiation. Participation in 

10 outdoor sports (e.g., basketball, soccer, golf, swimming, cycling) significantly increased 

11 UV radiation exposure (Thieden et al., 2004a; Thieden et al., 2004b; Moehrle, 2001; 

12 Moehrle et al., 2000). Occupations that substantially increased exposure to UV radiation 

13 included farming (Schenker et al., 2002; Airey et al., 1997), fishing (Rosenthal et al., 

14 1988), landscaping (Rosenthal et al., 1988), construction (Gies and Wright, 2003), 

15 physical education (Vishvakarman et al., 2001), mail delivery (Vishvakarman et al., 

16 2001), and various other occupations that require workers to spend the majority of their 

17 day outdoors during peak UV radiation hours.

18 Age and gender were found to be factors that influence human exposure to UV radiation, 

19 particularly by influencing other factors of exposure such as outdoor activity and risk 

20 behavior. Studies indicated that females generally spent less time outdoors and, 

21 consequently, had lower UV radiation exposure compared to males (Godar et al., 2001; 

22 Gies et al., 1998; Shoveller et al., 1998). The lowest exposure to UV radiation among 

23 Americans in the Godar et al. (2001) study was received in females during their child 

24 raising years (age 22-40 years); the highest exposure was observed in males aged 

25 41-59 years. A similar Canadian survey found that younger adult males had the greatest 

26 exposures to UV radiation (Shoveller et al., 1998).

27 Geography influences the degree of solar UV flux to the surface, and hence exposure to 

28 UV radiation. In the U.S. study by Godar et al. (2001), northerners and southerners were 

29 found to spend an equal amount of time outdoors; however, the higher solar flux at lower 

30 latitudes significantly increased the annual UV radiation dose for southerners. The annual 

31 UV radiation doses in southerners were 25 and 40% higher in females and males, 

32 respectively, compared to northerners. Other studies also have shown that altitude and 

33 latitude influence personal exposure to UV radiation (Rigel et al., 1999; Kimlin et al., 

34 1998).
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1 Protective behaviors such as using sunscreen (Nole and Johnson, 2004), wearing 

2 protective clothing (Rosenthal et al., 1988), and spending time in shaded areas (Moise et 

3 al., 1999) were shown to reduce exposure to UV radiation. In one study, the use of 

4 sunscreen was associated with extended intentional UV radiation exposure (Autier et al., 

5 1999); however, a follow-up study indicated that sunscreen use increased duration of 

6 exposures to doses of UV radiation that were below the threshold level for erythema 

7 (Autier et al., 2000).

8 Given these and other factors that potentially influence UV radiation exposure, the 2006 

9 O3 AQCD listed the following subpopulations potentially at risk for higher exposures to 

10 UV radiation:

11  Individuals who engage in high-risk behavior (e.g., sunbathing);

12  Individuals who participate in outdoor sports and activities;

13  Individuals who work outdoors with inadequate shade (e.g., farmers, 

14 construction workers, etc.); and

15  Individuals living in geographic areas with higher solar flux including lower 

16 latitudes (e.g., Honolulu, HI) and higher altitudes (e.g., Denver, CO).

17 The risks associated with all these factors are, of course, highly dependent on season and 

18 region (Sliney and Wengraitis, 2006).

10.4.3 Human Health Effects due to UV-B Radiation

19 Chapter 10 of the 2006 O3 AQCD covered in detail the human health effects associated 

20 with solar UV-B radiation exposure. These effects include erythema, skin cancer, ocular 

21 damage, and immune system suppression. These adverse effects, along with protective 

22 effects of UV radiation through increased production of vitamin D are summarized in this 

23 section. For additional details, the reader is referred to Chapter 10 of the 2006 O3 AQCD 

24 (U.S. EPA, 2006b) and references therein.

25 The most conspicuous and well-recognized acute response to UV radiation is erythema, 

26 or the reddening of the skin. Erythema is likely caused by direct damage to DNA by UV 

27 radiation (Matsumura and Ananthaswamy, 2004). Many studies discussed in the 2006 O3

28 AQCD found skin type to be a significant risk factor for erythema. Additional risk factors 

29 include atopic dermatitis (ten Berge et al., 2009).

30 Skin cancer is another prevalent health effect associated with UV radiation. Exposure to 

31 UV radiation is considered to be a major risk factor for all forms of skin cancer (Diepgen 

32 and Mahler, 2002; Gloster and Brodland, 1996). Ultraviolet radiation is especially 
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1 effective in inducing genetic mutations and acts as both a tumor initiator and promoter. 

2 Keratinocytes have evolved DNA repair mechanisms to correct the damage induced by 

3 UV; however, mutations can occur, leading to skin cancers that are appearing with 

4 increasing frequency (Hildesheim and Fornace, 2004). The relationship between skin 

5 cancer and chronic exposure to UV radiation is further explored in Chapter 10 of the 

6 2006 O3 AQCD (U.S. EPA, 2006b).

7 Ocular damage from UV radiation exposure includes effects on the cornea, lens, iris, and 

8 associated epithelial and conjunctival tissues. The region of the eye affected by exposure 

9 to UV radiation depends on the wavelength of the incident UV radiation. Depending on 

10 wavelength, common health effects associated with UV radiation include photokeratitis 

11 (snow blindness; short wavelengths) and cataracts (opacity of the lens; long 

12 wavelengths).

13 Experimental studies have shown that exposure to UV radiation may suppress local and 

14 systemic immune responses to a variety of antigens (Clydesdale et al., 2001; Garssen and 

15 Van Loveren, 2001; Selgrade et al., 1997). In rodent models, these effects have been 

16 shown to worsen the course and outcome of some infectious diseases and cancers 

17 (Granstein and Matsui, 2004; Norval et al., 1999). Results from human clinical studies 

18 suggest that immune suppression induced by UV radiation may be a risk factor 

19 contributing to skin cancer induction (Ullrich, 2005; Caforio et al., 2000; Lindelof et al., 

20 2000). There is also evidence that UV radiation has indirect involvement in viral 

21 oncogenesis through the human papillomavirus (Pfister, 2003), dermatomyositis (Okada 

22 et al., 2003), human immunodeficiency virus (Breuer-McHam et al., 2001) and other 

23 forms of immunosuppression (Selgrade et al., 2001).

24 A potential health benefit of increased UV-B exposure relates to the production of 

25 vitamin D in humans. Most humans depend on sun exposure to satisfy their requirements 

26 for vitamin D (Holick, 2004). Vitamin D deficiency can cause metabolic bone disease 

27 among children and adults, and also may increase the risk of many common chronic 

28 diseases, including type I diabetes mellitus and rheumatoid arthritis (Holick, 2004). 

29 Substantial in vitro and toxicological evidence also support a role for vitamin D activity 

30 against the incidence or progression of various forms of cancer (Giovannucci, 2005; John 

31 et al., 2005; Smedby et al., 2005; Grant and Garland, 2004; Hughes et al., 2004; 

32 Freedman et al., 2002; Grant, 2002a, b; John et al., 1999; Studzinski and Moore, 1995; 

33 Lefkowitz and Garland, 1994; Hanchette and Schwartz, 1992; Garland et al., 1990; 

34 Gorham et al., 1990). In some studies, UV-B related production of vitamin D had 

35 potential beneficial immunomodulatory effects on multiple sclerosis, insulin-dependent 

36 diabetes mellitus, and rheumatoid arthritis (Ponsonby et al., 2002; Cantorna, 2000). More 
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1 details on UV-B protective studies are provided in Chapter 10 of the 2006 O3 AQCD 

2 (U.S. EPA, 2006b).

3 In establishing guidelines on limits of exposure to UV radiation, the International 

4 commission on Non-Ionizing Radiation Protection (ICNIRP) agreed that some low-level 

5 exposure to UV radiation has health benefits (ICNIRP, 2004). However, the adverse 

6 health effects of higher UV exposures necessitated the development of exposure limits 

7 for UV radiation. The ICNIRP recognized the challenge in establishing exposure limits 

8 that would achieve a realistic balance between beneficial and adverse health effects. As 

9 concluded by ICNIRP (2004), “[t]he present understanding of injury mechanisms and 

10 long-term effects of exposure to [UV radiation] is incomplete, and awaits further 

11 research.”

10.4.4 Ecosystem and Materials Damage Effects Due to UV-B Radiation

12 A 2009 progress report on the environmental effects of O3 depletion from the UNEP, 

13 Environmental Effects Assessment Panel (UNEP, 2009) lists many ecosystem and 

14 materials damage effects from UV-B radiation. An in-depth assessment of the global 

15 ecosystem and materials damage effects from UV-B radiation per se is out of the scope of 

16 this assessment. However, a brief summary of some mid-latitude effects is provided in 

17 this section to provide context for UV-B related issues pertaining to tropospheric O3. The 

18 reader is referred to the UNEP report (UNEP, 2009) and references therein for further 

19 details. All of these UV-B related ecosystem and materials effects can also be influenced 

20 by climate change through temperature and other meteorological alterations, making 

21 quantifiable predictions of UV-B effects difficult.

22 Terrestrial ecosystem effects from increased UV-B radiation include reduced plant 

23 productivity and plant cover, changes in biodiversity, susceptibility to infection, and 

24 increases in natural UV protective responses. In general, however, these effects are small 

25 for moderate UV-B increases at mid-latitudes. A field study on wheat in southern Chile 

26 found no substantial changes in crop yield with moderate increases in UV-B radiation 

27 (Calderini et al., 2008). Similarly, field studies on silver birch (Betula pendula) in 

28 Finland found no significant effects in photosynthetic function with increases in UV-B 

29 radiation (Aphalo et al., 2009). Subtle, but important, changes in habitat and biodiversity 

30 have also been linked to increases in UV-B radiation (Mazza et al., 2010; Obara et al., 

31 2008; Wahl, 2008). Some plants have natural coping mechanisms for dealing with 

32 changes in UV-B radiation (Favory et al., 2009; Jenkins, 2009; Brown and Jenkins, 2008; 

33 Ioki et al., 2008), but these defenses may have costs in terms of reduced growth (Snell et 

34 al., 2009; Clarke and Robinson, 2008; Semerdjieva et al., 2003; Phoenix et al., 2000).
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1 Aquatic ecosystem effects from increased UV-B radiation include sensitivity in 

2 growth, immune response, and behavioral patterns of aquatic organisms. One study 

3 looking at coccolithophores, an abundant phytoplankton group, found a 25% reduction in 

4 cellular growth with UV-B exposure (Gao et al., 2009a). Exposure to relevant levels of 

5 UV-B radiation has been shown to modify immune response, blood chemistry, and 

6 behavior in certain species of fish (Markkula et al., 2009; Holtby and Bothwell, 2008; 

7 Jokinen et al., 2008). Adverse effects on growth and development from UV-B radiation 

8 have also been observed for amphibians, sea urchins, mollusks, corals, and zooplankton 

9 (Garcia et al., 2009; Romansic et al., 2009; Croteau et al., 2008a; Croteau et al., 2008b; 

10 Marquis et al., 2008; Marquis and Miaud, 2008; Oromi et al., 2008). Increases in the flux 

11 of UV-B radiation may also result in an increase in the catalysis of trace metals including 

12 mercury, particularly in clear oligotrophic lakes with low levels of dissolved organic 

13 carbon to stop the penetration of UV-B radiation (Schindler et al., 1996). This could then 

14 alter the mobility of trace metals including the potential for increased mercury 

15 volatilization and transport within and among ecosystems.

16 Biogeochemical cycles, particularly the carbon cycle, can also be influenced by 

17 increased UV-B radiation. A study on high latitude wetlands found UV-induced increases 

18 in CO2 uptake through soil respiration (Haapala et al., 2009) while studies on arid 

19 terrestrial ecosystems found evidence for UV-induced release of CO2 through 

20 photodegradation of above-ground plant litter (Brandt et al., 2009; Henry et al., 2008; 

21 Caldwell et al., 2007; Zepp et al., 2007). Changes in solar UV radiation may also have 

22 effects on carbon cycling and CO2 uptake in the oceans (Brewer and Peltzer, 2009; 

23 Meador et al., 2009; Fritz et al., 2008; Zepp et al., 2008; Hader et al., 2007) as well as 

24 release of dissolved organic matter from sediment and algae (Mayer et al., 2009; 

25 Riggsbee et al., 2008). Additional studies showing effects on these and additional 

26 biogeochemical cycles including the water cycle and halocarbon cycle can be found in 

27 the UNEP report (UNEP, 2009) and references therein.

28 Materials damage from increased UV-B radiation include UV-induced 

29 photodegradation of wood (Kataoka et al., 2007) and plastics (Pickett et al., 2008). These 

30 studies and others summarizing photo-resistant coatings and materials designed to reduce 

31 photodegradation of materials are summarized in the UNEP report (UNEP, 2009) and 

32 references therein.
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10.4.5 UV-B Related Effects Associated with Changes in Tropospheric 

Ozone Concentrations 

1 There are multiple complexities in attempting to quantify the relationship between 

2 changes in tropospheric O3 concentrations and UV radiation exposure. Quantifying the 

3 relationship between UV radiation and health or welfare effects is complicated by the 

4 uncertainties involved in the selection of an action spectrum and appropriate 

5 characterization of dose (e.g., peak or cumulative levels of exposure, timing of exposures, 

6 etc.) The lack of published studies that critically examine these issues together--that is the 

7 incremental health or welfare effects attributable specifically to UV-B changes resulting 

8 from reductions in tropospheric O3 concentrations--reflects the significant challenges in 

9 this field.

10 As reported in the 2006 O3 AQCD, one analysis by Lutter and Wolz (1997) attempted to 

11 estimate the effects of a nationwide 10 ppb reduction in seasonal average tropospheric O3

12 on the incidence of nonmelanoma and melanoma skin cancers and cataracts in humans. 

13 Their estimate, however, depended upon several simplifying assumptions, ranging from 

14 an assumed generalized 10-ppb reduction in O3 column density, national annual average 

15 incidence rates for the two types of skin cancer, and simple, linear biological 

16 amplification factors. Specifically, the decrease of 10 ppbv in seasonally averaged O3

17 concentrations is likely an overestimate since it doesn’t account for the influence of 

18 background O3 coming from the global accumulation or generation of regional chemistry 

19 (Adamowicz et al., 2004). Further, the methodologies used in this analysis have ignored 

20 area-specific factors that are important in estimating the extent to which small, variable 

21 changes in ground-level O3 mediate long-term exposures to UV-B radiation.

22 A more recent study by Madronich et al. (2011) used CMAQ to estimate UV radiation 

23 response to changes in tropospheric O3 under different control scenarios projected out to 

24 2020. This study focused on southeastern U.S. and accounted for spatial and temporal 

25 variation in tropospheric O3 reductions, an important consideration since most controls 

26 are focused on reducing O3 in populated urban areas. The contrasting control strategies 

27 considered in this study included a historical scenario designed to meet an 84 ppb 8-h 

28 daily max standard and a reduced scenario designed to bring areas predicted to exceed a 

29 similarly designed 70 ppb standard into attainment. A biologically effective irradiance 

30 was estimated by multiplying the modeled UV irradiance by a sensitivity function (action 

31 spectrum) for the induction of nonmelanoma skin cancer in mice corrected for human 

32 skin transmission, then integrating over UV wavelengths. The average relative change in 

33 skin cancer-weighted surface UV radiation between the two scenarios was about 0.11% 

34 over June, July and August. Weighting by population, this estimate increased to 0.19%. 

35 Madronich et al. (2011) report that their estimated UV radiation increment is an order of 
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1 magnitude less than that by Lutter and Wolz (1997) with the main reason for the 

2 discrepancy coming from the unrealistic uniform 10 ppb reduction in O3 assumed in the 

3 former study. Madronich et al. (2011) did not attempt to link their predicted increase in 

4 UV radiation to a predicted increase in skin cancer incidence, however, due to several 

5 remaining and substantial uncertainties.

6 A handful of additional studies have addressed the relationship between changes in 

7 tropospheric pollutant concentrations and UV-B radiation exposure, providing some 

8 additional insight. A study by Palancar and Toselli (2002) looked at changes in measured 

9 UV-B radiation in relation to ground-level air pollutants during several air pollution 

10 episodes in Cordoba, Argentina. They found that changes in aerosol concentrations 

11 explained the majority of UV-B radiation fluctuations, and that changes in tropospheric 

12 O3 and SO2 had little effect. Repapis et al. (1998) performed a similar study on UV-B 

13 exposures during high and low air pollution days in Athens, Greece. They found cloud 

14 cover and aerosols to be the major factors in observed UV-B exposures reductions. 

15 Studies by Acosta and Evans (2000) in Mexico City and Koronakis et al. (2002) in 

16 Athens, Greece both found significant reductions in surface-level UV exposures during 

17 pollution episodes. Both these studies include tropospheric O3 as a potential driver for the 

18 reductions, but neither study was able to quantify the influence of individual atmospheric 

19 components involved in the observed attenuation in UV-B radiation. 

20 In the absence of reliable studies specifically addressing UV-B related health effects from 

21 a reduction in tropospheric O3, inferences were made in the 2006 O3 AQCD on the basis 

22 of studies focused on stratospheric O3 depletion. Studies included in that review 

23 examined the potential effect of stratospheric O3 depletion on the risk of erythema 

24 (Longstreth et al., 1998), skin cancer (Urbach, 1997; Slaper et al., 1996; De Gruijl, 1995; 

25 Longstreth et al., 1995; Madronich and De Gruijl, 1993), nonmelanoma skin cancer 

26 (Slaper et al., 1996; Longstreth et al., 1995), and cataracts (Longstreth et al., 1995). Note 

27 that several of the concerns expressed above in relation to the Lutter and Wolz (1997)

28 analysis are relevant to these analyses as well. Furthermore, these studies have a high 

29 degree of uncertainty due to inadequate information on the action spectrum and dose30 response relationships. As a result, caution is advised when assessing and interpreting the 

31 quantitative results of health risks due to stratospheric O3 depletion in the context of 

32 tropospheric O3 shielding.

33 Although the UV-B related health effects attributed to marginal reductions in 

34 tropospheric or ground-level O3 that would result from reductions in O3 concentrations 

35 have not been directly assessed, they would be expected to be small given the above 

36 findings and the fact that tropospheric O3 makes up only ~10% of the total atmospheric 

37 O3 column at mid-latitudes (Kar et al., 2010). Furthermore, O3 present in the planetary 
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1 boundary layer makes up only ~10% of tropospheric O3 (Thompson et al., 2007) and the 

2 NAAQS has only a fractional influence on those ground-level O3 concentrations. The net 

3 result is a very small influence on total column O3 through attainment of the O3 standard. 

4 In addition, the health benefits of UV-B in the production of vitamin D suggests that 

5 increased risks of human disease due to a slight excess in UV-B radiation exposure may 

6 be offset by the benefits of enhanced vitamin D production. However, as with other 

7 impacts of UV-B on human health, this beneficial effect of UV-B has not been studied in 

8 sufficient detail to allow for a credible health benefits assessment. Hence, the above 

9 mentioned health and welfare effects associated with UV-B exposures resulting from 

10 changes in ground-level O3 concentrations would likely be small or nonexistent based on 

11 current information.

12 More reasonable estimates of the human health impacts of enhanced UV-B penetration 

13 following reduced ground-level O3 concentrations require both (a) a solid understanding 

14 of the multiple factors that define the extent of human exposure to UV-B, and (b) well15 defined and quantifiable links between human disease and UV-B exposure. Within the 

16 uncertain context of presently available information on UV-B surface fluxes, a risk 

17 assessment of UV-B-related health effects would need to factor in human habits (e.g., 

18 daily activities, recreation, dress, and skin care) in order to adequately estimate UV-B 

19 exposure levels. Little is known about the impact of variability in these human factors on 

20 individual exposure to UV radiation. Furthermore, detailed information does not exist 

21 regarding the relevant type (e.g., peak or cumulative) and time period (e.g., childhood, 

22 lifetime, or current) of exposure, wavelength dependency of biological responses, and 

23 inter-individual variability in UV resistance. In conclusion, the effect of changes in 

24 surface-level O3 concentrations on UV-induced health outcomes cannot yet be critically 

25 assessed within reasonable uncertainty. The reader is referred to the U.S. EPA 2002 Final 

26 Response to Court Remand (U.S. EPA, 2003) for detailed discussions of the data and 

27 scientific issues associated with the determination of public health benefits resulting from 

28 the attenuation of UV-B by surface-level O3.

10.5 Summary

10.5.1 Summary of the Effects of Tropospheric Ozone on Climate

29 Tropospheric O3 is a major greenhouse gas, third in importance after CO2 and CH4. 

30 While the developed world has successfully reduced emissions of O3 precursors in recent 

31 decades, many developing countries have experienced large increases in precursor 

32 emissions and these trends are expected to continue, at least in the near term. Projections 
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of radiative forcing due to changing O3 over the 21st 1 century show wide variation, due in 

2 large part to the uncertainty of future emissions of source gases. In the near-term (2000-

2030), projections of O3 radiative forcing range from near zero to +0.3 W/m2 3 , depending 

4 on the emissions scenario (Stevenson et al., 2006). Reduction of tropospheric O3

5 concentrations could therefore provide an important means to slow climate change in 

6 addition to the added benefit improving surface air quality.

7 It is clear that increases in tropospheric O3 lead to warming. However the precursors of 

8 O3 also have competing effects on the greenhouse gas CH4, complicating emissions 

9 reduction strategies. A decrease in CO or VOC emissions would enhance OH 

10 concentrations, shortening the lifetime of CH4, while a decrease in NOX emissions could 

11 depress OH concentrations in certain regions and lengthen the CH4 lifetime. Recent 

12 research, however, has indicated that a carefully combined reduction of CO, VOCs, and 

13 NOX emissions could lead to net cooling (Naik et al., 2005). They calculate that such 

14 reductions would have the greatest impact for developing countries in tropical regions.

15 Abatement of CH4 emissions would likely provide the most straightforward means to 

16 address climate change since CH4 is itself an important precursor of background O3

17 (West et al., 2007; West et al., 2006; Fiore et al., 2002). A reduction of CH4 emissions 

18 would also improve air quality on its own right. A set of global abatement measures 

19 identified by West and Fiore (2005) could reduce CH4 emissions by 10% at a cost 

20 savings, decrease background O3 by about 1 ppb in the Northern Hemisphere summer, 

and lead to a global net cooling of 0.12 W/m2 21 . Unlike measures to reduce NOX, which 

22 would have immediate impacts on surface O3 but little net radiative forcing, the cooling 

23 effects of CH4 controls would be realized gradually, over ~12 years. West et al. (2007)

24 explored further the benefits of CH4 abatement, finding that a 20% reduction in global 

25 CH4 emissions would lead to significantly greater cooling per unit reduction in surface 

26 O3, compared to 20% reductions in VOCs or CO.

27 Important uncertainties remain regarding the impact of tropospheric O3 on future climate 

28 change. To address these uncertainties, further research is needed to: (1) enhance our 

29 knowledge of the natural atmosphere; (2) interpret observed trends of O3 in the free 

30 troposphere and remote regions; (3) improve our understanding of the CH4 budget, 

31 especially emissions from wetlands and agricultural sources, (4) understand the 

32 relationship between regional O3 radiative forcing and regional climate change; and (5) 

33 determine the optimal mix of emissions reductions that would act to limit future climate 

34 change.
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10.5.2 Summary of UV-B Related Effects on Human Health, Ecosystems, 

and Materials Relating to Changes in Tropospheric Ozone 

Concentrations

1 UV radiation emitted from the Sun contains sufficient energy when it reaches the Earth to 

2 break (photolyze) chemical bonds in molecules, thereby leading to damaging effects on 

3 living organisms and materials. Atmospheric O3 plays a crucial role in reducing exposure 

4 to solar UV radiation at the Earth’s surface. Ozone in the stratosphere is responsible for 

5 the majority of this shielding effect, as approximately 90% of total atmospheric O3 is 

6 located there over mid-latitudes. Ozone in the troposphere provides supplemental 

7 shielding of radiation in the wavelength band from 280-315 nm, referred to as UV-B 

8 radiation. UV-B radiation has important effects on human health and ecosystems, and is 

9 associated with materials damage.

10 Adverse human health effects associated with solar UV-B radiation exposure include 

11 erythema, skin cancer, ocular damage, and immune system suppression. A potential 

12 human health benefit of increased UV-B exposure involves the UV-induced production 

13 of vitamin D which may help reduce the risk of metabolic bone disease, type I diabetes, 

14 mellitus, and rheumatoid arthritis, and may provide beneficial immunomodulatory effects 

15 on multiple sclerosis, insulin-dependent diabetes mellitus, and rheumatoid arthritis.

16 Adverse ecosystem and materials damage effects associated with solar UV-B radiation 

17 exposure include terrestrial and aquatic ecosystem impacts, alteration of biogeochemical 

18 cycles, and degradation of man-made materials. Terrestrial ecosystem effects from 

19 increased UV-B radiation include reduced plant productivity and plant cover, changes in 

20 biodiversity, susceptibility to infection, and increases in natural UV protective responses. 

21 In general, however, these effects are small for moderate UV-B increases at mid22 latitudes. Aquatic ecosystem effects from increased UV-B radiation include sensitivity in 

23 growth, immune response, and behavioral patterns of aquatic organisms and the potential 

24 for increased catalysis and mobility of trace metals. Biogeochemical cycles, particularly 

25 the carbon cycle, can also be influenced by increased UV-B radiation with effects ranging 

26 from UV-induced increases in CO2 uptake through soil respiration to UV-induced release 

27 of CO2 through photodegradation of above-ground plant litter. Changes in solar UV 

28 radiation may also have effects on carbon cycling and CO2 uptake in the oceans as well 

29 as release of dissolved organic matter from sediment and algae. Finally, materials damage 

30 from increased UV-B radiation includes UV-induced photodegradation of wood and 

31 plastic.

32 There is a lack of published studies that critically examine the incremental health or 

33 welfare effects (adverse or beneficial) attributable specifically to changes in UV-B 

34 exposure resulting from perturbations in tropospheric O3 concentrations. While the 
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1 effects are expected to be small, they cannot yet be critically assessed within reasonable 

2 uncertainty.

10.6 References

Acosta, LR; Evans, WFJ. (2000). Design of the Mexico City UV monitoring network: UV-B measurements at 

ground level in the urban environment. J Geophys Res 105: 5017-5026. 

http://dx.doi.org/10.1029/1999JD900250.

Adamowicz, V; Dales, R; Hale, BA; Hrudey, SE; Krupnick, A; Lippman, M; McConnell, J; Renzi, P. (2004). 

Report of an expert panel to review the socio-economic models and related components supporting the 

development of Canada-Wide Standards (CWS) for particulate matter (PM) and ozone to the Royal 

Society of Canada. J Toxicol Environ Health B Crit Rev 7: 147-266. 

http://dx.doi.org/10.1080/10937400490253238.

Airey, DK; Wong, JCF; Fleming, RA; Meldrum, LR. (1997). An estimate of the UV-B exposure for outdoor 

workers during a south-east Queensland summer. Health Phys 72: 544-549. 

Aphalo, PJ; Vapaavuori, EM; de la Rosa, TM; Lehto, T. (2009). Does supplemental UV-B radiation affect gas 

exchange and RuBisCO activity of Betula pendula Roth. seedlings grown in forest soil under 

greenhouse conditions? Plant Ecol Divers 2: 37-43. http://dx.doi.org/10.1080/17550870902780299.

Arrhenius, S. (1896). On the influence of carbonic acid in the air upon the temperature of the ground. Philos 

Mag 41: 237-276. 

Autier, P; Dore, JF; Negrier, S; Lienard, D; Panizzon, R; Lejeune, FJ; Guggisberg, D; Eggermont, AM. (1999). 

Sunscreen use and duration of sun exposure: A double-blind, randomized trial. J Natl Cancer Inst 91: 

1304-1309. 

Autier, P; Dore, JF; Reis, AC; Grivegnee, A; Ollivaud, L; Truchetet, F; Chamoun, E; Rotmensz, N; Severi, G; 

Cesarini, JP. (2000). Sunscreen use and intentional exposure to ultraviolet A and B radiation: A double 

blind randomized trial using personal dosimeters. Br J Cancer 83: 1243-1248. 

Balis, DS; Zerefos, CS; Kourtidis, K; Bais, AF; Hofzumahaus, A; Kraus, A; Schmitt, R; Blumthaler, M; Gobbi, GP.

(2002). Measurements and modeling of photolysis rates during the photochemical activity and 

ultraviolet radiation (PAUR) II campaign. J Geophys Res 107: 8138. 

http://dx.doi.org/10.1029/2000JD000136.

Berntsen, TK; Myhre, G; Stordal, F; Isaksen, ISA. (2000). Time evolution of tropospheric ozone and its radiative 

forcing. J Geophys Res 105: 8915-8930. http://dx.doi.org/10.1029/1999JD901139.

Boer, GJ; Yu, B. (2003). Climate sensitivity and response. Clim Dynam 20: 415-429. 

http://dx.doi.org/10.1007/s00382-002-0283-3.

Bony, S; Colman, R; Kattsov, VM; Allan, RP; Bretherton, CS; Dufresne, JL; Hall, A; Hallegatte, S; Holland, MM; 

Ingram, W; Randall, DA; Soden, BJ; Tselioudis, G; Webb, MJ. (2006). How well do we understand and 

evaluate climate change feedback processes? J Clim 19: 3445-3482. 

Brandt, LA; Bohnet, C; King, JY. (2009). Photochemically induced carbon dioxide production as a mechanism 

for carbon loss from plant litter in arid ecosystems. J Geophys Res 114: G02004. 

http://dx.doi.org/10.1029/2008jg000772.

Breuer-McHam, J; Simpson, E; Dougherty, I; Bonkobara, M; Ariizumi, K; Lewis, DE; Dawson, DB; Duvic, M; 

Cruz, PD, Jr. (2001). Activation of HIV in human skin by ultraviolet B radiation and its inhibition by 

NF"kappa"B blocking agents. Photochem Photobiol 74: 805-810. 

Brewer, PG; Peltzer, ET. (2009). Limits to marine life. Science 324: 347-348. 

http://dx.doi.org/10.1126/science.1170756.

Brown, BA; Jenkins, GI. (2008). UV-B signaling pathways with different fluence-rate response profiles are 

distinguished in mature Arabidopsis leaf tissue by requirement for UVR8, HY5, and HYH. Plant Physiol 

146: 576-588. http://dx.doi.org/10.1104/pp.107.108456.

Bruhl, C; Crutzen, PJ. (1989). On the disproportionate role of tropospheric ozone as a filter against solar UV-B 

radiation. Geophys Res Lett 16: 703-706. http://dx.doi.org/10.1029/GL016i007p00703.
Draft – Do Not Cite or Quote 10-31 September 2011

Caforio, ALP; Fortina, AB; piaserico, S; Alaibac, M; Tona, F; Feltrin, G; Pompei, E; Testolin, L; Gambino, A; 

Volta, SD; Thiene, G; Casarotto, D; Peserico, A. (2000). Skin cancer in heart transplant recipients: risk 

factor analysis and relevance of immunosuppressive therapy. Circulation 102: III-222 - III-227. 

Calderini, DF; Lizana, XC; Hess, S; Jobet, CR; Zuniga, JA. (2008). Grain yield and quality of wheat under 

increased ultraviolet radiation (UV-B) at later stages of the crop cycle. J Agr Sci 146: 57-64. 

http://dx.doi.org/10.1017/S0021859607007447.

Caldwell, MM; Bornman, JF; Ballare, CL; Flint, SD; Kulandaivelu, G. (2007). Terrestrial ecosystems, increased 

solar ultraviolet radiation, and interactions with bother climate change factors. Photochem Photobiol Sci 

6: 252-266. http://dx.doi.org/10.1039/B700019g.

Cantorna, MT. (2000). Vitamin D and autoimmunity: Is vitamin D status an environmental factor affecting 

autoimmune disease prevalence? Exp Biol Med 223: 230-233. 

Chang, W; Liao, H; Wang, H. (2009). Climate responses to direct radiative forcing of anthropogenic aerosols, 

tropospheric ozone, and long-lived greenhouse gases in eastern China over 1951-2000. Adv Atmos Sci 

26: 748-762. http://dx.doi.org/10.1007/s00376-009-9032-4.

Christiansen, B. (1999). Radiative forcing and climate sensitivity: The ozone experience. Q J Roy Meteorol Soc 

125: 3011-3035. http://dx.doi.org/10.1002/qj.49712556011.

Clarke, LJ; Robinson, SA. (2008). Cell wall-bound ultraviolet-screening compounds explain the high ultraviolet 

tolerance of the Antarctic moss, Ceratodon purpureus. New Phytol 179: 776-783. 

http://dx.doi.org/10.1111/j.1469-8137.2008.02499.x.

Clydesdale, GJ; Dandie, GW; Muller, HK. (2001). Ultraviolet light induced injury: Immunological and 

inflammatory effects. Immunol Cell Biol 79: 547-568. 

Cooper, OR; Parrish, DD; Stohl, A; Trainer, M; Nedelec, P; Thouret, V; Cammas, JP; Oltmans, SJ; Johnson, BJ; 

Tarasick, D; Leblanc, T; McDermid, IS; Jaffe, D; Gao, R; Stith, J; Ryerson, T; Aikin, K; Campos, T; 

Weinheimer, A; Avery, MA. (2010). Increasing springtime ozone mixing ratios in the free troposphere 

over western North America. Nature 463: 344-348. http://dx.doi.org/10.1038/nature08708.

Crist, KC; Carmichael, GR; John, K. (1994). UV-B exposure and atmospheric ozone - Evaluation of radiative 

flux to changes in ambient ozone levels. J Hazard Mater 37: 527-538. http://dx.doi.org/10.1016/0304-

3894(93)E0096-K.

Croteau, MC; Martyniuk, CJ; Trudeau, VL; Lean, DRS. (2008a). Chronic exposure of rana pipiens tadpoles to 

uvb radiation and the estrogenic chemical 4-tert-octylphenol. J Toxicol Environ Health A 71: 134-144. 

Croteau, MC; Davidson, MA; Lean, DRS; Trudeau, VL. (2008b). Global increases in ultraviolet B radiation: 

Potential impacts on amphibian development and metamorphosis. Physiol Biochem Zool 81: 743-761. 

http://dx.doi.org/10.1086/591949.

De Gruijl, FR. (1995). Action spectrum for photocarcinogenesis. Recent Results Cancer Res 139: 21-30. 

Derwent, RG; Collins, WJ; Johnson, CE; Stevenson, DS. (2001). Transient behaviour of tropospheric ozone 

precursors in a global 3-D CTM and their indirect greenhouse effects. Clim Change 49: 463-487. 

Diepgen, TL; Mahler, V. (2002). The epidemiology of skin cancer. Br J Dermatol 146: 1-6. 

Favory, JJ; Stec, A; Gruber, H; Rizzini, L; Oravecz, A; Funk, M; Albert, A; Cloix, C; Jenkins, GI; Oakeley, EJ; 

Seidlitz, HK; Nagy, F; Ulm, R. (2009). Interaction of COP1 and UVR8 regulates UV-B-induced 

photomorphogenesis and stress acclimation in Arabidopsis. EMBO J 28: 591-601. 

http://dx.doi.org/10.1038/emboj.2009.4.

Fiore, AM; Jacob, DJ; Field, BD; Streets, DG; Fernandes, SD; Jang, C. (2002). Linking ozone pollution and 

climate change: The case for controlling methane. Geophys Res Lett 29: 1919. 

http://dx.doi.org/10.1029/2002GL015601.

Fiore, AM; West, JJ; Horowitz, LW; Naik, V; Schwartzkopf, MD. (2008). Characterizing the tropospheric ozone 

response to methane emission controls and the benefits to climate and air quality. J Geophys Res 113: 

D08307. http://dx.doi.org/10.1029/2007JD009162.

Fishman, J; Fakhruzzaman, K; Cros, B; Nganga, D. (1991). Identification of widespread pollution in the 

Southern Hemisphere deduced from satellite analyses. Science 252: 1693-1696. 

http://dx.doi.org/10.1126/science.252.5013.1693.
Draft – Do Not Cite or Quote 10-32 September 2011

Forster, P; Ramaswamy, V; Artaxo, P; Berntsen, T; Betts, R; Fahey, DW; Haywood, J; Lean, J; Lowe, DC; 

Myhre, G; Nganga, J; Prinn, R; Raga, G; Schultz, M; Van Dorland, R. (2007). Changes in atmospheric 

constituents and in radiative forcing. In S Solomon; D Qin; M Manning; Z Chen; M Marquis; KB Averyt; 

M Tignor; HL Miller (Eds.), Climate Change 2007: The physical science basis: Contribution of Working 

Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (pp. 129-

234). Cambridge, U.K. and New York, NY: Cambridge University Press.

Freedman, DM; Dosemeci, M; McGlynn, K. (2002). Sunlight and mortality from breast, ovarian, colon, prostate, 

and non-melanoma skin cancer: A composite death certificate based case-control study. Occup Environ 

Med 59: 257-262. 

Fritz, JJ; Neale, PJ; Davis, RF; Peloquin, JA. (2008). Response of Antarctic phytoplankton to solar UVR 

exposure: Inhibition and recovery of photosynthesis in coastal and pelagic assemblages. Mar Ecol 

Prog Ser 365: 1-16. http://dx.doi.org/10.3354/Meps07610.

Fuglestvedt, JS; Berntsen, TK; Isaksen, ISA; Mao, H; Liang, X, -Z; Wang, W, -C. (1999). Climatic forcing of 

nitrogen oxides through changes in tropospheric ozone and methane: Global 3D model studies. Atmos 

Environ 33: 961-978. http://dx.doi.org/10.1016/S1352-2310(98)00217-9.

Fusco, AC; Logan, JA. (2003). Analysis of 1970-1995 trends in tropospheric ozone at Northern Hemisphere 

midlatitudes with the GEOS-CHEM model. J Geophys Res 108: 4449. 

http://dx.doi.org/10.1029/2002JD002742.

Gao, KS; Ruan, ZX; Villafane, VE; Gattuso, JP; Helbling, EW. (2009a). Ocean acidification exacerbates the 

effect of UV radiation on the calcifying phytoplankter Emiliania huxleyi. Limnol Oceanogr 54: 1855-

1862. 

Garcia, TS; Paoletti, DJ; Blaustein, AR. (2009). Correlated trait responses to multiple selection pressures in 

larval amphibians reveal conflict avoidance strategies. Freshw Biol 54: 1066-1077. 

http://dx.doi.org/10.1111/j.1365-2427.2008.02154.x.

Garland, FC; Garland, CF; Gorham, ED; Young, JF. (1990). Geographic variation in breast cancer mortality in 

the United States: A hypothesis involving exposure to solar radiation. Prev Med 19: 614-622. 

Garssen, J; Van Loveren, H. (2001). Effects of ultraviolet exposure on the immune system. Crit Rev Immunol 

21: 359-397. 

Gauss, M; Myhre, G; Isaksen, ISA; Grewe, V; Pitari, G; Wild, O; Collins, WJ; Dentener, FJ; Ellingsen, K; Gohar, 

LK; Hauglustaine, DA; Iachetti, D; Lamarque, JF; Mancini, E; Mickley, LJ; Prather, MJ; Pyle, JA; 

Sanderson, MG; Shine, KP; Stevenson, DS; Sudo, K; Szopa, S; Zeng, G. (2006). Radiative forcing 

since preindustrial times due to ozone change in the troposphere and the lower stratosphere. Atmos 

Chem Phys 6: 575-599. 

Gies, P; Roy, C; Toomey, S; MacLennan, R; Watson, M. (1998). Solar UVR exposures of primary school 

children at three locations in Queensland. Photochem Photobiol 68: 78-83. 

Gies, P; Wright, J. (2003). Measured solar ultraviolet radiation exposures of outdoor workers in Queensland in 

the building and construction industry. Photochem Photobiol 78: 342-348. 

Giovannucci, E. (2005). The epidemiology of vitamin D and cancer incidence and mortality: A review (United 

States) [Review]. Cancer Causes Control 16: 83-95. 

Gloster, HM, Jr; Brodland, DG. (1996). The epidemiology of skin cancer. Dermatol Surg 22: 217-226. 

Godar, DE; Wengraitis, SP; Shreffler, J; Sliney, DH. (2001). UV doses of Americans. Photochem Photobiol 73: 

621-629. 

Gorham, ED; Garland, FC; Garland, CF. (1990). Sunlight and breast cancer incidence in the USSR. Int J 

Epidemiol 19: 820-824. http://dx.doi.org/10.1093/ije/19.4.820.

Granstein, RD; Matsui, MS. (2004). UV radiation-induced immunosuppression and skin cancer. Cutis 5: 4-9. 

Grant, WB. (2002a). An ecologic study of dietary and solar ultraviolet-B links to breast carcinoma mortality rates. 

Cancer 94: 272-281. 

Grant, WB. (2002b). An estimate of premature cancer mortality in the US due to inadequate doses of solar 

ultraviolet-B radiation. Cancer 94: 1867-1875. 

Grant, WB; Garland, CF. (2004). A critical review of studies on vitamin D in relation to colorectal cancer 

[Review]. Nutr Cancer 48: 115-123. 

Haapala, JK; Morsky, SK; Saarnio, S; Rinnan, R; Suokanerva, H; Kyr, E; Latola, K; Martikanen, PJ; Holopainen, 

T; Silvola, J. (2009). Carbon dioxide balance of a fen ecosystem in northern Finland under elevated 

UV-B radiation. Global Change Biol 15: 943-954. http://dx.doi.org/10.1111/j.1365-2486.2008.01785.x.
Draft – Do Not Cite or Quote 10-33 September 2011

Hader, DP; Kumar, HD; Smith, RC; Worrest, RC. (2007). Effects of solar UV radiation on aquatic ecosystems 

and interactions with climate change. Photochem Photobiol Sci 6: 267-285. 

http://dx.doi.org/10.1039/B700020k.

Hanchette, CL; Schwartz, GG. (1992). Geographic patterns of prostate cancer mortality. Cancer 70: 2861-2869. 

Hansen, J; Sato, M; Ruedy, R; Nazarenko, L; Lacis, A; Schmidt, GA; Russell, G; Aleinov, I; Bauer, M; Bauer, S; 

Bell, N; Cairns, B; Canuto, V; Chandler, M; Cheng, Y; Del Genio, A; Faluvegi, G; Fleming, E; Friend, A; 

Hall, T; Jackman, C; Kelley, M; Kiang, N; Koch, D; Lean, J; Lerner, J; Lo, K; Menon, S; Miller, R; Minnis, 

P; Novakov, T; Oinas, V; Perlwitz, J; Rind, D; Romanou, A; Shindell, D; Stone, P; Sun, S; Tausnev, N; 

Thresher, D; Wielicki, B; Wong, T; Yao, M; Zhang, S. (2005). Efficacy of climate forcings. J Geophys 

Res 110: D18104. http://dx.doi.org/10.1029/2005JD005776.

Hansen, JE; Sato, M; Ruedy, R. (1997). Radiative forcing and climate response. J Geophys Res 102: 6831-

6864. http://dx.doi.org/10.1029/96JD03436.

Harvey, LDD. (2004). Characterizing the annual-mean climatic effect of anthropogenic CO2 and aerosol 

emissions in eight coupled atmosphere-ocean GCMs. Clim Dynam 23: 569-599. 

http://dx.doi.org/10.1007/s00382-004-0455-4.

Held, IM; Soden, BJ. (2000). Water vapor feedback and global warming. Annual Review of Energy and the 

Environment 25: 441-475. 

Henry, HAL; Brizgys, K; Field, CB. (2008). Litter decomposition in a california annual grassland: Interactions 

between photodegradation and litter layer thickness. Ecosystems 11: 545-554. 

http://dx.doi.org/10.1007/s10021-008-9141-4.

Hildesheim, J; Fornace, AJ, Jr. (2004). The dark side of light: The damaging effects of UV rays and the 

protective efforts of MAP kinase signaling in the epidermis. DNA Repair 3: 567-580. 

Holick, MF. (2004). Sunlight and vitamin D for bone health and prevention of autoimmune diseases, cancers, 

and cardiovascular disease. Am J Clin Nutr 80: 1678S-1688S. 

Holland, MM; Bitz, CM. (2003). Polar amplification of climate change in coupled models. Clim Dynam 21: 221-

232. http://dx.doi.org/10.1007/s00382-003-0332-6.

Holtby, LB; Bothwell, ML. (2008). Effects of solar ultraviolet radiation on the behaviour of juvenile coho salmon 

(Oncorhynchus kisutch): Avoidance, feeding, and agonistic interactions. Can J Fish Aquat Sci 65: 701-

711. http://dx.doi.org/10.1139/F08-013.

Hughes, AM; Armstrong, BK; Vajdic, CM; Turner, J; Grulich, AE; Fritschi, L; Milliken, S; Kaldor, J; Benke, G; 

Kricker, A. (2004). Sun exposure may protect against non-Hodgkin lymphoma: A case-control study. Int 

J Cancer 112: 865-871. 

ICNIRP. (International Commission on Non-Ionizing Radiation Protection). (2004). Guidelines on limits of 

exposure to ultraviolet radiation of wavelengths between 180 nm and 400 nm (incoherent optical 

radiation). In ICNIRP Guidelines (Vol. 87, pp. 171-186). Oberschleissheim, Germany.

Ioki, M; Takahashi, S; Nakajima, N; Fujikura, K; Tamaoki, M; Saji, H; Kubo, A; Aono, M; Kanna, M; Ogawa, D; 

Fukazawa, J; Oda, Y; Yoshida, S; Watanabe, M; Hasezawa, S; Kondo, N. (2008). An unidentified 

ultraviolet-B-specific photoreceptor mediates transcriptional activation of the cyclobutane pyrimidine 

dimer photolyase gene in plants. Planta 229: 25-36. http://dx.doi.org/10.1007/s00425-008-0803-4.

IPCC. (Intergovernmental Panel on Climate Change). (2000). Special report on emissions scenarios: A special 

report of Working Group III of the Intergovernmental Panel on Climate Change. Cambridge, UK: 

Intergovernmental Panel on Climate Change; Cambridge University Press. 

http://www.grida.no/climate/ipcc/emission/.

IPCC. (Intergovernmental Panel on Climate Change). (2007b). Summary for policymakers. In: The Physical 

Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the 

Intergovernmental Panel on Climate Change. In Climate Change 2007. Cambridge, United Kingdom 

and New York, NY, USA: Cambridge University Press. 

http://www.ipcc.ch/publications_and_data/ar4/wg2/en/spm.html.

Isaksen, ISA; Berntsen, TK; Wang, WC. (2001). NOx emissions from aircraft: Its impact on the global 

distribution of CH4 and O3 and on radiative forcing. Terr Atmos Ocean Sci 12: 63-78. 

Ito, A; Sudo, K; Akimoto, H; Sillman, S; Penner, JE. (2007a). Global modeling analysis of tropospheric ozone 

and its radiative forcing from biomass burning emissions in the twentieth century. J Geophys Res 112: 

D24307. http://dx.doi.org/10.1029/2007JD008745.
Draft – Do Not Cite or Quote 10-34 September 2011

Jaffe, D; Price, H; Parrish, D; Goldstein, A; Harris, J. (2003). Increasing background ozone during spring on the 

west coast of North America. Geophys Res Lett 30: 1613. http://dx.doi.org/10.1029/2003GL017024.

Jenkins, GI. (2009). Signal transduction in responses to UV-B radiation. Annu Rev Plant Biol 60: 407-431. 

http://dx.doi.org/10.1146/annurev.arplant.59.032607.092953.

John, EM; Schwartz, GG; Dreon, DM; Koo, J. (1999). Vitamin D and breast cancer risk: the NHANES I 

Epidemiologic Follow-up Study, 1971-1975 to 1992. Cancer Epidemiol Biomarkers Prev 8: 399-406. 

John, EM; Schwartz, GG; Koo, J; Van Den Berg, D; Ingles, SA. (2005). Sun exposure, vitamin D receptor gene 

polymorphisms, and risk of advanced prostate cancer. Cancer Res 65: 5470-5479. 

http://dx.doi.org/10.1158/0008-5472.CAN-04-3134.

Jokinen, IE; Markkula, ES; Salo, HM; Kuhn, P; Nikoskelainen, S; Arts, MT; Browman, HI. (2008). Exposure to 

increased ambient ultraviolet B radiation has negative effects on growth, condition and immune 

function of juvenile Atlantic salmon (Salmo salar). Photochem Photobiol 84: 1265-1271. 

http://dx.doi.org/10.1111/j.1751-1097.2008.00358.x.

Jonson, JE; Simpson, D; Fagerli, H; Solberg, S. (2005). Can we explain the trends in European ozone levels? 

Atmos Chem Phys 6: 51-66. http://dx.doi.org/10.5194/acp-6-51-2006.

Joshi, M; Shine, KP; Ponater, M; Stuber, N; Sausen, R; Li. (2003). A comparison of climate response to different 

radiative forcings in three general circulation models: Towards an improved metric of climate change. 

Clim Dynam 20: 843-854. http://dx.doi.org/10.1007/s00382-003-0305-9.

Kar, J; Fishman, J; Creilson, JK; Richter, A; Ziemke, J; Chandra, S. (2010). Are there urban signatures in the 

tropospheric ozone column products derived from satellite measurements? Atmos Chem Phys 10: 

5213-5222. http://dx.doi.org/10.5194/acp-10-5213-2010.

Kataoka, Y; Kiguchi, M; Williams, RS; Evans, PD. (2007). Violet light causes photodegradation of wood beyond 

the zone affected by ultraviolet radiation. Holzforschung und Holzverwertung 61: 23-27. 

http://dx.doi.org/10.1515/HF.2007.005.

Kiehl, JT; Schneider, TL; Portmann, RW; Solomon, S. (1999). Climate forcing due to tropospheric and 

stratospheric ozone. J Geophys Res 104: 31239-31254. http://dx.doi.org/10.1029/1999JD900991.

Kimlin, MG; Wong, JCF; Parisi, AV. (1998). Simultaneous comparison of the personal UV exposure of two 

human groups at different altitudes. Health Phys 74: 429-434. 

Kloster, S; Dentener, F; Feichter, J; Raes, F; Lohmann, U; Roeckner, E; Fischer-bruns, I. (2009). A GCM study 

of future climate response to aerosol pollution reductions. Clim Dynam 34: 1177-1194. 

http://dx.doi.org/10.1007/s00382-009-0573-0.

Koronakis, PS; Sfantos, GK; Paliatsos, AG; Kaldellis, JK; Garofalakis, JE; Koronaki, IP. (2002). Interrelations of 

UV-global/global/diffuse solar irradiance components and UV-global attenuation on air pollution episode 

days in Athens, Greece. Atmos Environ 36: 3173-3181. 

Lacis, AA; Wuebbles, DJ; Logan, JA. (1990). Radiative forcing of climate by changes in the vertical distribution 

of ozone. J Geophys Res 95: 9971-9981. http://dx.doi.org/10.1029/JD095iD07p09971.

Lamarque, JF; Hess, P; Emmons, L; Buja, L; Washington, W; Granier, C. (2005). Tropospheric ozone evolution 

between 1890 and 1990. J Geophys Res 110: D08304. http://dx.doi.org/10.1029/2004JD005537.

Lamarque, JF; Bond, TC; Eyring, V; Granier, C; Heil, A; Klimont, Z; Lee, D; Liousse, C; Mieville, A; Owen, B; 

Schultz, MG; Shindell, D; Smith, SJ; Stehfest, E; Van Aardenne, J; Cooper, OR; Kainuma, M; 

Mahowald, N; McConnell, JR; Naik, V; Riahi, K; van Vuuren, DP. (2010). Historical (1850–2000) 

gridded anthropogenic and biomass burning emissions of reactive gases and aerosols: Methodology 

and application. Atmos Chem Phys Discuss 10: 4963-5019. http://dx.doi.org/10.5194/acpd-10-4963-

2010.

Lee, EH; Tingey, DT; Hogsett, WE; Laurence, JA. (2003a). History of tropospheric ozone for the San Bernardino 

Mountains of southern California, 1963-1999. Atmos Environ 37: 2705-2717. 

http://dx.doi.org/10.1016/S1352-2310(03)00203-6.

Lefkowitz, ES; Garland, CF. (1994). Sunlight, vitamin D, and ovarian cancer mortality rates in US women. Int J 

Epidemiol 23: 1133-1136. 

Lelieveld, J; van Aardenne, J; Fischer, H; de Reus, M; Williams, J; Winkler, P. (2004). Increasing ozone over the 

Atlantic Ocean. Science 304: 1483-1487. http://dx.doi.org/10.1126/science.1096777.

Lenoble, J. (1993). Atmospheric radiative transfer. In. Hampton, VA: A. Deepak Publishing.
Draft – Do Not Cite or Quote 10-35 September 2011

Levy, H, II; Schwaarzkopf, MD; Horowitz, L; Ramaswamy, V; Findell, KL. (2008). Strong sensitivity of late 21st 

century climate to projected changes in short-lived air pollutants. J Geophys Res 113: D06102. 

http://dx.doi.org/10.1029/2007JD009176.

Liao, H; Seinfeld, JH; Adams, PJ; Mickley, LJ. (2004b). Global radiative forcing of coupled tropospheric ozone 

and aerosols in a unified general circulation model. J Geophys Res 109: D16207. 

http://dx.doi.org/10.1029/2003JD004456.

Lindelof, B; Sigurgeirsson, B; Gabel, H; Stern, RS. (2000). Incidence of skin cancer in 5356 patients following 

organ transplantation. Br J Dermatol 143: 513-519. 

Logan, JA; Megretskaia, IA; Miller, AJ; Tiao, GC; Choi, D; Zhang, L; Stolarski, RS; Labow, GJ; Hollandsworth, 

SM; Bodeker, GE; Claude, H; De Muer, D; Kerr, JB; Tarasick, DW; Oltmans, SJ; Johnson, B; Schmidlin, 

F; Staehelin, J; Viatte, P; Uchino, O. (1999). Trends in the vertical distribution of ozone: A comparison 

of two analyses of ozonesonde data. J Geophys Res 104: 26373-26399. 

http://dx.doi.org/10.1029/1999JD900300.

Longstreth, J; de Gruijl, FR; Kripke, ML; Abseck, S; Arnold, F; Slaper, HI; Velders, G; Takizawa, Y; van der 

Leun, JC. (1998). Health risks. J Photochem Photobiol B 46: 20-39. 

Longstreth, JD; Gruijl, D; Kripke, ML; Takizawa, Y; van der Leun, JC. (1995). Effects of increased solar 

ultraviolet radiation on human health. Ambio 24: 153-165. 

Lutter, R; Wolz, C. (1997). UV-B screening by tropospheric ozone: Implications for the national ambient air 

quality standard. Environ Sci Technol 31: 142A-146A. 

Madronich, S; De Gruijl, F. (1993). Skin cancer and UV radiation [Letter/Response]. Nature 366: 23. 

http://dx.doi.org/10.1038/366023a0.

Madronich, S; Wagner, M; Groth, P. (2011). Influence of tropospheric ozone control on exposure to ultraviolet 

radiation at the surface. Environ Sci Technol 45: 6919-6923. http://dx.doi.org/10.1021/es200701q.

Marenco, A; Gouget, H; Nédélec, P; Pagés, J, -P; Karcher, F. (1994). Evidence of a long-term increase in 

tropospheric ozone from Pic du Midi data series: Consequences: Positive radiative forcing. J Geophys 

Res 99: 16617-16632. http://dx.doi.org/10.1029/94JD00021.

Markkula, E; Salo, HM; Rikalainen, K; Jokinen, IE. (2009). Long-term UVB irradiation affects the immune 

functions of carp (Cyprinus carpio) and rainbow trout (Oncorhynchus mykiss). Photochem Photobiol 85: 

347-352. http://dx.doi.org/10.1111 ⁄ j.1751-1097.2008.00446.x.

Marquis, O; Miaud, C; Lena, JP. (2008). Developmental responses to UV-B radiation in common frog Rana 

temporaria embryos from along an altitudinal gradient. Population Ecology 50: 123-130. 

http://dx.doi.org/10.1007/s10144-007-0071-3.

Marquis, O; Miaud, C. (2008). Variation in UV sensitivity among common frog Rana temporaria populations 

along an altitudinal gradient. Zoology (Jena) 111: 309-317. http://dx.doi.org/10.1016/j.zool.2007.09.003.

Matsumura, Y; Ananthaswamy, HN. (2004). Toxic effects of ultraviolet radiation on the skin. Toxicol Appl 

Pharmacol 195: 298-308. 

Mayer, LM; Schick, LL; Hardy, KR; Estapa, ML. (2009). Photodissolution and other photochemical changes 

upon irradiation of algal detritus. Limnol Oceanogr 54: 1688-1698. 

Mazza, CA; Izaguirre, MM; Curiale, J; Ballare, CL. (2010). A look into the invisible: Ultraviolet-B sensitivity in an 

insect (Caliothrips phaseoli) revealed through a behavioural action spectrum. Proc Biol Sci 277: 367-

373. http://dx.doi.org/10.1098/rspb.2009.1565.

Meador, JA; Baldwin, AJ; Catala, P; Jeffrey, WH; Joux, F; Moss, JA; Pakulski, JD; Stevens, R; Mitchell, DL.

(2009). Sunlight-induced DNA damage in marine micro-organisms collected along a latitudinal gradient 

from 70 degrees N to 68 degrees S. Photochem Photobiol 85: 412-421. 

http://dx.doi.org/10.1111/j.1751-1097.2008.00462.x.

Mickley, LJ; Leibensperger, EM; Jacob, DJ; Rind, D. (In Press) Regional warming from aerosol removal over the 

United States: Results from a transient 2010-2050 climate simulation. Atmos Environ. 

http://dx.doi.org/10.1016/j.atmosenv.2011.07.030.

Mickley, LJ; Murti, PP; Jacob, DJ; Logan, JA; Koch, DM; Rind, D. (1999). Radiative forcing from tropospheric 

ozone calculated with a unified chemistry-climate model. J Geophys Res 104: 30153-30172. 

http://dx.doi.org/10.1029/1999JD900439.

Mickley, LJ; Jacob, DJ; Rind, D. (2001). Uncertainty in preindustrial abundance of tropospheric ozone: 

Implications for radiative forcing calculations. J Geophys Res 106: 3389-3399. 

http://dx.doi.org/10.1029/2000JD900594.
Draft – Do Not Cite or Quote 10-36 September 2011

Mickley, LJ; Jacob, DJ; Field, BD; Rind, D. (2004). Climate response to the increase in tropospheric ozone since 

preindustrial times: A comparison between ozone and equivalent CO2 forcings. J Geophys Res 109: 

D05106. http://dx.doi.org/10.1029/2003JD003653.

Moehrle, M; Heinrich, L; Schmid, A; Garbe, C. (2000). Extreme UV exposure of professional cyclists. 

Dermatology 201: 44-45. 

Moehrle, M. (2001). Ultraviolet exposure in the Ironman triathlon. Med Sci Sports Exerc 33: 1385-1386. 

Moise, AF; Buttner, PG; Harrison, SL. (1999). Sun exposure at school. Photochem Photobiol 70: 269-274. 

Naik, V; Mauzerall, D; Horowitz, L; Schwarzkopf, MD; Ramaswamy, V; Oppenheimer, M. (2005). Net radiative 

forcing due to changes in regional emissions of tropospheric ozone precursors. J Geophys Res 110: 

D24306. http://dx.doi.org/10.1029/2005JD005908.

Naja, M; Akimoto, H. (2004). Contribution of regional pollution and long-range transport to the Asia-Pacific 

region: Analysis of long-term ozonesonde data over Japan. J Geophys Res 109: D21306. 

http://dx.doi.org/10.1029/2004JD004687.

Nole, G; Johnson, AW. (2004). An analysis of cumulative lifetime solar ultraviolet radiation exposure and the 

benefits of daily sun protection. Dermatol Ther 17: 57-62. 

Norval, M; Garssen, J; Van Loveren, H; El-Ghorr, AA. (1999). UV-induced changes in the immune response to 

microbial infections in human subjects and animal models. J Epidemiol 6: S84-S92. 

NRC. (National Research Council). (2005). Radiative forcing of climate change: Expanding the concept and 

addressing uncertainties. In. Washington, DC: The National Academies Press.

Obara, Y; Koshitaka, H; Arikawa, K. (2008). Better mate in the shade: Enhancement of male mating behaviour 

in the cabbage butterfly, Pieris rapae crucivora, in a UV-rich environment. J Exp Biol 211: 3698-3702. 

http://dx.doi.org/10.1242/jeb.021980.

Okada, S; Weatherhead, E; Targoff, IN; Wesley, R; Miller, FW; Group, IMCS. (2003). Global surface ultraviolet 

radiation intensity may modulate the clinical and immunologic expression of autoimmune muscle 

disease. Arthritis Rheum 48: 2285-2293. 

Oltmans, SJ; Lefohn, AS; Harris, JM; Galbally, I; Scheel, HE; Bodeker, G; Brunke, E; Claude, H; Tarasick, D; 

Johnson, BJ; Simmonds, P; Shadwick, D; Anlauf, K; Hayden, K; Schmidlin, F; Fujimoto, T; Akagi, K; 

Meyer, C; Nichol, S; Davies, J; Redondas, A; Cuevas, E. (2006). Long-term changes in tropospheric 

ozone. Atmos Environ 40: 3156-3173. http://dx.doi.org/10.1016/j.atmosenv.2006.01.029.

Ordonez, C; Brunner, D; Staehelin, J; Hadjinicolaou, P; Pyle, JA; Jonas, M; Wernli, H; Prevot, ASH. (2007). 

Strong influence of lowermost stratospheric ozone on lower tropospheric background ozone changes 

over Europe. Geophys Res Lett 34: L07805. http://dx.doi.org/10.1029/2006GL029113.

Oromi, N; Marquis, O; Miaud, C; Sanuy, D. (2008). Influence of ambient ultraviolet radiation on Bufo calamita 

egg development in a semiarid zone (Catalonia, Spain). J Environ Biol 29: 135-137. 

Palancar, GG; Toselli, BM. (2002). Erythemal ultraviolet irradiance in Cordoba, Argentina. Atmos Environ 36: 

287-292. 

Pavelin, EG; Johnson, CE; Rughooputh, S; Toumi, R. (1999). Evaluation of pre-industrial surface ozone 

measurements made using Schonbein's method. Atmos Environ 33: 919-929. 

http://dx.doi.org/10.1016/S1352-2310(98)00257-X.

Pfister, H. (2003). Human papillomavirus and skin cancer. J Natl Cancer Inst Monographs No. 31: 52-56. 

Philipona, R; Behrens, K; Ruckstuhl, C. (2009). How declining aerosols and rising greenhouse gases forced 

rapid warming in Europe since the 1980s. Geophys Res Lett 36: L02806. 

http://dx.doi.org/10.1029/2008GL036350.

Phoenix, GK; Gwynn-Jones, D; Lee, JA; Callaghan, TV. (2000). The impacts of UV-B radiation on the 

regeneration of a sub-arctic heath community. Plant Ecol 146: 67-75. 

http://dx.doi.org/10.1023/A:1009839506658.

Pickett, JE; Gibson, DA; Gardner, MM. (2008). Effects of irradiation conditions on the weathering of engineering 

thermoplastics. Polym Degrad Stabil 93: 1597-1606. 

http://dx.doi.org/10.1016/j.polymdegradstab.2008.02.009.

Ponsonby, AL; McMichael, A; Van der Mei, I. (2002). Ultraviolet radiation and autoimmune disease: Insights 

from epidemiological research. Toxicology 181/182: 71-78. 

Repapis, CC; Mantis, HT; Paliatsos, AG; Philandras, CM; Bais, AF; Meleti, C. (1998). Case study of UV-B 

modification during episodes of urban air pollution. Atmos Environ 38: 2203-2208. 
Draft – Do Not Cite or Quote 10-37 September 2011

Rigel, DS; Rigel, EG; Rigel, AC. (1999). Effects of altitude and latitude on ambient UVB radiation. J Am Acad 

Dermatol 40: 114-116. 

Riggsbee, JA; Orr, CH; Leech, DM; Doyle, MW; Wetzel, RG. (2008). Suspended sediments in river ecosystems: 

Photochemical sources of dissolved organic carbon, dissolved organic nitrogen, and adsorptive 

removal of dissolved iron. J Geophys Res 113: G03019. http://dx.doi.org/10.1029/2007jg000654.

Rind, D; Healy, R; Parkinson, C; Martinson, D. (1995). The role of sea ice in 2×CO2 climate model sensitivity. 

Part I: The total influence of sea ice thickness and extent. J Clim 8: 449-463. 

http://dx.doi.org/10.1175/1520-0442(1995)008<0449:TROSII>2.0.CO;2.

Romansic, JM; Waggener, AA; Bancroft, BA; Blaustein, AR. (2009). Influence of ultraviolet-B radiation on 

growth, prevalence of deformities, and susceptibility to predation in Cascades frog (Rana cascadae) 

larvae. Hydrobiologia 624: 219-233. http://dx.doi.org/10.1007/s10750-009-9703-2.

Rosenthal, FS; Phoon, C; Bakalian, AE; Taylor, HR. (1988). The ocular dose of ultraviolet radiation to outdoor 

workers. Invest Ophthalmol Vis Sci 29: 649-656. 

Ruckstuhl, C; Philipona, R; Behrens, K; Coen, MC; Dürr, B; Heimo, A; Mätzler, C; Nyeki, S; Ohmura, A; 

Vuilleumier, L; Weller, M; Wehrli, C; Zelenka, A. (2008). Aerosol and cloud effects on solar brightening 

and recent rapid warming. Geophys Res Lett 35: L12708. http://dx.doi.org/10.1029/2008GL034228.

Schenker, MB; Orenstein, MR; Samuels, SJ. (2002). Use of protective equipment among California farmers. Am 

J Ind Med 42: 455-464. 

Schindler, DW; Curtis, PJ; Parker, BR; Stainton, MP. (1996). Consequences of climate warming and lake 

acidification for UV-B penetration in North American boreal lakes. Nature 379: 705-708. 

http://dx.doi.org/10.1038/379705a0.

Selgrade, M, -JK; Smith, MV; Oberhelman-Bragg, LJ; LeVee, GJ; Koren, HS; Cooper, KD. (2001). Dose 

response for UV-induced immune suppression in people of color: Differences based on erythemal 

reactivity rather than skin pigmentation. Photochem Photobiol 74: 88-95. 

Selgrade, MK; Repacholi, MH; Koren, HS. (1997). Ultraviolet radiation-induced immune modulation: Potential 

consequences for infectious, allergic, and autoimmune disease. Environ Health Perspect 105: 332-334. 

Semerdjieva, SI; Phoenix, GK; Hares, D; Gwynn-Jones, D; Callaghan, TV; Sheffield, E. (2003). Surface 

morphology, leaf and cuticle thickness of four dwarf shrubs from a sub-Arctic heath following long-term 

exposure to enhanced levels of UV-B. Physiol Plant 117: 289-294. http://dx.doi.org/10.1034/j.1399-

3054.2003.00006.x.

Shindell, D; Faluvegi, G; Lacis, A; Hansen, J; Ruedy, R; Aguilar, E. (2006). Role of tropospheric ozone 

increases in 20th-century climate change. J Geophys Res 111: D08302. 

http://dx.doi.org/10.1029/2005JD006348.

Shindell, D; Faluvegi, G. (2009). Climate response to regional radiative forcing during the twentieth century. Nat 

Geosci 2: 294-300. http://dx.doi.org/10.1038/ngeo473.

Shindell, DT; Faluvegi, G. (2002). An exploration of ozone changes and their radiative forcing prior to the 

chlorofluorocarbon era. Atmos Chem Phys Discuss 2: 363-374. http://dx.doi.org/10.5194/acp-2-363-

2002.

Shindell, DT; Faluvegi, G; Bell, N. (2003). Preindustrial-to-present-day radiative forcing by tropospheric ozone 

from improved simulations with the GISS chemistry-climate GCM. Atmos Chem Phys 3: 1675-1702. 

http://dx.doi.org/10.5194/acp-3-1675-2003.

Shindell, DT; Faluvegi, G; Bell, N; Schmidt, GA. (2005). An emissions-based view of climate forcing by methane 

and tropospheric ozone. Geophys Res Lett 32: L04803. http://dx.doi.org/10.1029/2004GL021900.

Shindell, DT; Faluvegi, G; Bauer, SE; Koch, DM; Unger, N; Menon, S; Miller, RL; Schmidt, GA; Streets, DG.

(2007). Climate response to projected changes in short-lived species under an A1B scenario from 

2000-2050 in the GISS climate model. J Geophys Res 112: D20103. 

http://dx.doi.org/10.1029/2007jd008753.

Shindell, DT; Levy H, II; Schwarzkopf, MD; Horowitz, LW; Lamarque, JF; Faluvegi, G. (2008). Multimodel 

projections of climate change from short-lived emissions due to human activities. J Geophys Res 113: 

D11109. http://dx.doi.org/10.1029/2007JD009152.

Shoveller, JA; Lovato, CY; Peters, L; Rivers, JK. (1998). Canadian national survey on sun exposure & protective 

behaviours: Adults at leisure. Cancer Prev Control 2: 111-116. 
Draft – Do Not Cite or Quote 10-38 September 2011

Simmonds, PG; Derwent, RG; Manning, AL; Spain, G. (2004). Significant growth in surface ozone at Mace 

Head, Ireland, 1987-2003. Atmos Environ 38: 4769-4778. 

http://dx.doi.org/10.1016/j.atmosenv.2004.04.036.

Sitch, S; Cox, PM; Collins, WJ; Huntingford, C. (2007). Indirect radiative forcing of climate change through 

ozone effects on the land-carbon sink. Nature 448: 791-794. http://dx.doi.org/10.1038/nature06059.

Slaper, H; Velders, GJM; Daniel, JS; de Gruijl, FR; Van der Leun, JC. (1996). Estimates of ozone depletion and 

skin cancer incidence to examine the Vienna Convention achievements. Nature 384: 256-258. 

Sliney, DH; Wengraitis, S. (2006). Is a differentiated advice by season and region necessary? Prog Biophys Mol 

Biol 92: 150-160. http://dx.doi.org/10.1016/j.pbiomolbio.2006.02.007.

Smedby, KE; Hjalgrim, H; Melbye, M; Torrang, A; Rostgaard, K; Munksgaard, L; Adami, J; Hansen, M; PorwitMacDonald, A; Jensen, BA; Roos, G; pedersen, BB; Sundstrom, C; Glimelius, B; Adami, H, -O. (2005). 

Ultraviolet radiation exposure and risk of malignant lymphomas. J Natl Cancer Inst 97: 199-209. 

Snell, KRS; Kokubun, T; Griffiths, H; Convey, P; Hodgson, DA; Newsham, KK. (2009). Quantifying the metabolic 

cost to an Antarctic liverwort of responding to an abrupt increase in UVB radiation exposure. Global 

Change Biol 15: 2563-2573. http://dx.doi.org/10.1111/j.1365-2486.2009.01929.x.

Soden, BJ; Held, IM. (2006). An assessment of climate feedbacks in coupled ocean-atmosphere models. J Clim 

19: 3354-3360. 

Staehelin, J; Thudium, J; Buehler, R; Volz-Thomas, A; Graber, W. (1994). Trends in surface ozone 

concentrations at Arosa (Switzerland). Atmos Environ 28: 75-87. http://dx.doi.org/10.1016/1352-

2310(94)90024-8.

Stevenson, DS. (2004). Radiative forcing from aircraft NO emissions: Mechanisms and seasonal dependence. J 

Geophys Res 109: D17307. http://dx.doi.org/10.1029/2004JD004759.

Stevenson, DS; Dentener, FJ; Schultz, MG; Ellingsen, K; Van Noije, TPC; Wild, O; Zeng, G; Amann, M; 

Atherton, CS; Bell, N; Bergmann, DJ; Bey, I; Butler, T; Cofala, J; Collins, WJ; Derwent, RG; Doherty, 

RM; Drevet, J; Eskes, HJ; Fiore, AM; Gauss, M; Hauglustaine, DA; Horowitz, LW; Isaksen, ISA; Krol, 

MC; Lamarque, JF; Lawrence, MG; Montanaro, V; Muller, JF; Pitari, G; Prather, MJ; Pyle, JA; Rast, S; 

Rodriguez, JM; Sanderson, MG; Savage, NH; Shindell, DT; Strahan, SE; Sudo, K; Szopa, S. (2006). 

Multimodel ensemble simulations of present-day and near-future tropospheric ozone. J Geophys Res 

111: D08301. http://dx.doi.org/10.1029/2005JD006338.

Studzinski, GP; Moore, DC. (1995). Sunlight--can it prevent as well as cause cancer? Cancer Res 55: 4014-

4022. 

Tanimoto, H. (2009). Increase in springtime tropospheric ozone at a mountainous site in Japan for the period 

1998-2006. Atmos Environ 43: 1358-1363. http://dx.doi.org/10.1016/j.atmosenv.2008.12.006.

Tarasick, DW; Fioletov, VE; Wardle, DI; Kerr, JB; Davies, J. (2005). Changes in the vertical distribution of ozone 

over Canada from ozonesondes: 1980–2001. J Geophys Res 110: D02304. 

http://dx.doi.org/10.1029/2004JD004643.

ten Berge, O; van Weelden, H; Bruijnzeel-Koomen, C; de Bruin-Weller, MS; Sigurdsson, V. (2009). Throwing a 

light on photosensitivity in atopic dermatitis: A retrospective study. Am J Clin Dermatol 10: 119-123. 

http://dx.doi.org/10.2165/00128071-200910020-00004.

Thieden, E; Philipsen, PA; Sandby-Moller, J; Heydenreich, J; Wulf, HC. (2004a). Proportion of lifetime UV dose 

received by children, teenagers and adults based on time-stamped personal dosimetry. J Invest 

Dermatol 123: 1147-1150. 

Thieden, E; Philipsen, PA; Heydenreich, J; Wulf, HC. (2004b). UV radiation exposure related to age, sex, 

occupation, and sun behavior based on time-stamped personal dosimeter readings. Arch Dermatol 

140: 197-203. 

Thompson, AM. (1992). The oxidizing capacity of the Earth's atmosphere: Probable past and future changes. 

Science 256: 1157-1165. http://dx.doi.org/10.1126/science.256.5060.1157.

Thompson, AM; Chappellaz, JA; Fung, IY; Kucsera, TL. (1993). The atmospheric CH4 increase since the last 

glacial maximum (2) Interactions with oxidants. Tellus B Chem Phys Meteorol 45: 242-257. 

http://dx.doi.org/10.1034/j.1600-0889.1993.t01-2-00003.x.

Thompson, AM; Hudson, RD. (1999). Tropical tropospheric ozone (TTO) maps from Nimbus 7 and Earth Probe 

TOMS by the modified-residual method: Evaluation with sondes, ENSO signals, and trends from 

Atlantic regional time series. J Geophys Res 104: 26961-26975. 

http://dx.doi.org/10.1029/1999JD900470.
Draft – Do Not Cite or Quote 10-39 September 2011

Thompson, AM; Stone, JB; Witte, JC; Miller, SK; Oltmans, SJ; Kucsera, TL; Ross, KL; Pickering, KE; Merrill, JT; 

Forbes, G; Tarasick, DW; Joseph, E; Schmidlin, FJ; McMillan, WW; Warner, J; Hintsa, EJ; Johnson, JE.

(2007). Intercontinental Chemical Transport Experiment Ozonesonde Network study (IONS) 2004: 2 

Tropospheric ozone budgets and variability over northeastern North America. J Geophys Res 112: 

D12S13. http://dx.doi.org/10.1029/2006JD007670.

U.S. EPA. (U.S. Environmental Protection Agency). (2003). National ambient air quality standards for ozone: 

Final response to remand. Fed Reg 68: 614-645. 

U.S. EPA. (U.S. Environmental Protection Agency). (2006b). Air quality criteria for ozone and related 

photochemical oxidants. (EPA/600/R-05/004AF). Research Triangle Park, NC: U.S. Environmental 

Protection Agency, Office of Research and Development. 

http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=149923.

Ullrich, SE. (2005). Mechanisms underlying UV-induced immune suppression. Mutat Res 571: 185-205. 

http://dx.doi.org/10.1016/j.mrfmmm.2004.06.059.

UNEP. (United Nations Environment Programme). (2009). Environmental effects of ozone depletion and its 

interactions with climate change. Nairobi, Kenya. 

http://ozone.unep.org/Assessment_Panels/EEAP/EEAP-Progress-report-2009.pdf.

Unger, N. (2006). Cross influences of ozone and sulfate precursor emissions changes on air quality and climate. 

PNAS 103: 4377-4380. http://dx.doi.org/10.1073/pnas.0508769103.

Unger, N; Shindell, DT; Koch, DM; Streets, DG. (2008). Air pollution radiative forcing from specific emissions 

sectors at 2030. J Geophys Res 113: D02306. http://dx.doi.org/10.1029/2007JD008683.

Unger, N; Bond, TC; Wang, JS; Koch, DM; Menon, S; Shindell, DT; Bauer, S. (2010). Attribution of climate 

forcing to economic sectors. PNAS 107: 3382-3387. http://dx.doi.org/10.1073/pnas.0906548107.

Urbach, F. (1997). Ultraviolet radiation and skin cancer of humans. J Photochem Photobiol B 40: 3-7. 

Van Aardenne, JA; Dentener, FJ; Olivier, JGJ; Klein Goldewijk, CGM; Lelieveld, J. (2001). A 1×1 resolution data 

set of historical anthropogenic trace gas emissions for the period 1890–1990. Global Biogeochem 

Cycles 15: 909-928. http://dx.doi.org/10.1029/2000GB001265.

Vishvakarman, D; Wong, JCF; Boreham, BW. (2001). Annual occupational exposure to ultraviolet radiation in 

central Queensland. Health Phys 81: 536-544. 

Volz, A; Kley, D. (1988). Evaluation of the Montsouris series of ozone measurements made in the nineteenth 

century. Nature 332: 240-242. http://dx.doi.org/10.1038/332240a0.

Wahl, M. (2008). Ecological modulation of environmental stress: Interactions between ultraviolet radiation, 

epibiotic snail embryos, plants and herbivores. J Anim Ecol 77: 549-557. 

http://dx.doi.org/10.1111/j.1365-2656.2007.01352.x.

Wang, W, -C; Pinto, JP; Yung, YL. (1980). Climatic effects due to halogenated compounds in the earth's 

atmosphere. J Atmos Sci 37: 333-338. http://dx.doi.org/10.1175/1520-

0469(1980)037<0333:CEDTHC>2.0.CO;2.

West, JJ; Fiore, AM. (2005). Management of tropospheric ozone by reducing methane emissions. Environ Sci 

Technol 39: 4685-4691. 

West, JJ; Fiore, AM; Horowitz, LW; Mauzerall, DL. (2006). Global health benefits of mitigating ozone pollution 

with methane emission controls. PNAS 103: 3988-3993. http://dx.doi.org/10.1073/pnas.0600201103.

West, JJ; Fiore, AM; Naik, V; Horowitz, LW; Schwarzkopf, MD; Mauzerall, DL. (2007). Ozone air quality and 

radiative forcing consequences of changes in ozone precursor emissions. Geophys Res Lett 34: 

L06806. http://dx.doi.org/10.1029/2006GL029173.

Wild, O; Prather, MJ; Akimoto, H. (2001). Indirect long-term global radiative cooling from NOX emissions. 

Geophys Res Lett 28: 1719-1722. http://dx.doi.org/10.1029/2000GL012573.

Worden, HM; Bowman, KW; Worden, JR; Eldering, A; Beer, R. (2008). Satellite measurements of the clear-sky 

greenhouse effect from tropospheric ozone. Nat Geosci 1: 305-308. http://dx.doi.org/10.1038/ngeo182.

Yang, X; Cox, RA; Warwick, NJ; Pyle, JA; Carver, GD; O'connor, FM; Savage, NH. (2005c). Tropospheric 

bromine chemistry and its impacts on ozone: A model study. J Geophys Res 110: D23311. 

http://dx.doi.org/10.1029/2005JD006244.

Zepp, RG; Erickson, DJ; Paul, ND; Sulzberger, B. (2007). Interactive effects of solar UV radiation and climate 

change on biogeochemical cycling. In The Environmental Effects of Ozone Depletion and its 

Interactions with Climate Change: 2006 Assessment. Nairobi , Kenya: United Nations Environment 

Programme.
Draft – Do Not Cite or Quote 10-40 September 2011

Zepp, RG; Shank, GC; Stabenau, E; Patterson, KW; Cyterski, M; Fisher, W; Bartels, E; Anderson, SL. (2008). 

Spatial and temporal variability of solar ultraviolet exposure of coral assemblages in the Florida Keys: 

Importance of colored dissolved organic matter. Limnol Oceanogr 53: 1909-1922. 

Zerefos, CS; Kourtidis, KA; Melas, D; Balis, D; Zanis, P; Katsaros, L; Mantis, HT; Repapis, C; Isaksen, I; 

Sundet, J; Herman, J; Bhartia, PK; Calpini, B. (2002). Photochemical activity and solar ultraviolet 

radiation (PAUR) modulation factors: An overview of the project. J Geophys Res 107: 8134. 

http://dx.doi.org/10.1029/2000JD000134.

Ziemke, JR; Chandra, S; Bhartia, PK. (2005). A 25‐year data record of atmospheric ozone in the Pacific from 

Total Ozone Mapping Spectrometer (TOMS) cloud slicing: Implications for ozone trends in the 

stratosphere and troposphere. J Geophys Res 110: D15105. http://dx.doi.org/10.1029/2004JD005687.